diff --git a/distribution/changelog.txt b/distribution/changelog.txt
index a800039df6..13c0ca1a18 100644
--- a/distribution/changelog.txt
+++ b/distribution/changelog.txt
@@ -10,6 +10,7 @@
 - Feature: [#15294] New vehicle animation type: flying animal.
 - Fix: [#13465] Creating a scenario based on a won save game results in a scenario that’s instantly won.
 - Fix: [#14316] Closing the Track Designs Manager window causes broken state.
+- Fix: [#14649] ImageImporter incorrectly remaps colours outside the RCT2 palette.
 - Fix: [#14667] “Extreme Hawaiian Island” has unpurchaseable land tiles (original bug).
 - Fix: [#15096] Crash when placing entrances in the scenario editor near the map corner.
 - Fix: [#15142] ToonTowner's mine roofs were moved into the pirate theme scenery group instead of the mine theme scenery group.
diff --git a/src/openrct2/drawing/ImageImporter.cpp b/src/openrct2/drawing/ImageImporter.cpp
index fe7b313872..3f578faf49 100644
--- a/src/openrct2/drawing/ImageImporter.cpp
+++ b/src/openrct2/drawing/ImageImporter.cpp
@@ -217,24 +217,22 @@ int32_t ImageImporter::CalculatePaletteIndex(
 {
     auto& palette = StandardPalette;
     auto paletteIndex = GetPaletteIndex(palette, rgbaSrc);
-    if (mode == IMPORT_MODE::CLOSEST || mode == IMPORT_MODE::DITHERING)
+    if ((mode == IMPORT_MODE::CLOSEST || mode == IMPORT_MODE::DITHERING) && !IsInPalette(palette, rgbaSrc))
     {
-        if (paletteIndex == PALETTE_TRANSPARENT && !IsTransparentPixel(rgbaSrc))
-        {
-            paletteIndex = GetClosestPaletteIndex(palette, rgbaSrc);
-        }
-    }
-    if (mode == IMPORT_MODE::DITHERING)
-    {
-        if (!IsTransparentPixel(rgbaSrc) && IsChangablePixel(GetPaletteIndex(palette, rgbaSrc)))
+        paletteIndex = GetClosestPaletteIndex(palette, rgbaSrc);
+        if (mode == IMPORT_MODE::DITHERING)
         {
             auto dr = rgbaSrc[0] - static_cast<int16_t>(palette[paletteIndex].Red);
             auto dg = rgbaSrc[1] - static_cast<int16_t>(palette[paletteIndex].Green);
             auto db = rgbaSrc[2] - static_cast<int16_t>(palette[paletteIndex].Blue);
 
+            // We don't want to dither remappable colours with nonremappable colours, etc
+            PaletteIndexType thisIndexType = GetPaletteIndexType(paletteIndex);
+
             if (x + 1 < width)
             {
-                if (!IsTransparentPixel(rgbaSrc + 4) && IsChangablePixel(GetPaletteIndex(palette, rgbaSrc + 4)))
+                if (!IsInPalette(palette, rgbaSrc + 4)
+                    && thisIndexType == GetPaletteIndexType(GetClosestPaletteIndex(palette, rgbaSrc + 4)))
                 {
                     // Right
                     rgbaSrc[4] += dr * 7 / 16;
@@ -247,8 +245,8 @@ int32_t ImageImporter::CalculatePaletteIndex(
             {
                 if (x > 0)
                 {
-                    if (!IsTransparentPixel(rgbaSrc + 4 * (width - 1))
-                        && IsChangablePixel(GetPaletteIndex(palette, rgbaSrc + 4 * (width - 1))))
+                    if (!IsInPalette(palette, rgbaSrc + 4 * (width - 1))
+                        && thisIndexType == GetPaletteIndexType(GetClosestPaletteIndex(palette, rgbaSrc + 4 * (width - 1))))
                     {
                         // Bottom left
                         rgbaSrc[4 * (width - 1)] += dr * 3 / 16;
@@ -258,7 +256,8 @@ int32_t ImageImporter::CalculatePaletteIndex(
                 }
 
                 // Bottom
-                if (!IsTransparentPixel(rgbaSrc + 4 * width) && IsChangablePixel(GetPaletteIndex(palette, rgbaSrc + 4 * width)))
+                if (!IsInPalette(palette, rgbaSrc + 4 * width)
+                    && thisIndexType == GetPaletteIndexType(GetClosestPaletteIndex(palette, rgbaSrc + 4 * width)))
                 {
                     rgbaSrc[4 * width] += dr * 5 / 16;
                     rgbaSrc[4 * width + 1] += dg * 5 / 16;
@@ -267,8 +266,8 @@ int32_t ImageImporter::CalculatePaletteIndex(
 
                 if (x + 1 < width)
                 {
-                    if (!IsTransparentPixel(rgbaSrc + 4 * (width + 1))
-                        && IsChangablePixel(GetPaletteIndex(palette, rgbaSrc + 4 * (width + 1))))
+                    if (!IsInPalette(palette, rgbaSrc + 4 * (width + 1))
+                        && thisIndexType == GetPaletteIndexType(GetClosestPaletteIndex(palette, rgbaSrc + 4 * (width + 1))))
                     {
                         // Bottom right
                         rgbaSrc[4 * (width + 1)] += dr * 1 / 16;
@@ -279,6 +278,7 @@ int32_t ImageImporter::CalculatePaletteIndex(
             }
         }
     }
+
     return paletteIndex;
 }
 
@@ -304,23 +304,40 @@ bool ImageImporter::IsTransparentPixel(const int16_t* colour)
 }
 
 /**
- * @returns true if pixel index is an index not used for remapping.
+ * @returns true if this colour is in the standard palette.
+ */
+bool ImageImporter::IsInPalette(const GamePalette& palette, int16_t* colour)
+{
+    return !(GetPaletteIndex(palette, colour) == PALETTE_TRANSPARENT && !IsTransparentPixel(colour));
+}
+
+/**
+ * @returns true if palette index is an index not used for a special purpose.
  */
 bool ImageImporter::IsChangablePixel(int32_t paletteIndex)
 {
-    if (paletteIndex == PALETTE_TRANSPARENT)
-        return true;
-    if (paletteIndex == 0)
-        return false;
+    PaletteIndexType entryType = GetPaletteIndexType(paletteIndex);
+    return entryType != PaletteIndexType::Special && entryType != PaletteIndexType::PrimaryRemap;
+}
+
+/**
+ * @returns the type of palette entry this is.
+ */
+ImageImporter::PaletteIndexType ImageImporter::GetPaletteIndexType(int32_t paletteIndex)
+{
+    if (paletteIndex <= 9)
+        return PaletteIndexType::Special;
+    if (paletteIndex >= 230 && paletteIndex <= 239)
+        return PaletteIndexType::Special;
+    if (paletteIndex == 255)
+        return PaletteIndexType::Special;
+    if (paletteIndex >= 243 && paletteIndex <= 254)
+        return PaletteIndexType::PrimaryRemap;
     if (paletteIndex >= 202 && paletteIndex <= 213)
-        return false;
-    if (paletteIndex == 226)
-        return false;
-    if (paletteIndex >= 227 && paletteIndex <= 229)
-        return false;
-    if (paletteIndex >= 243)
-        return false;
-    return true;
+        return PaletteIndexType::SecondaryRemap;
+    if (paletteIndex >= 46 && paletteIndex <= 57)
+        return PaletteIndexType::TertiaryRemap;
+    return PaletteIndexType::Normal;
 }
 
 int32_t ImageImporter::GetClosestPaletteIndex(const GamePalette& palette, const int16_t* colour)
diff --git a/src/openrct2/drawing/ImageImporter.h b/src/openrct2/drawing/ImageImporter.h
index e121414259..70e61b046f 100644
--- a/src/openrct2/drawing/ImageImporter.h
+++ b/src/openrct2/drawing/ImageImporter.h
@@ -50,6 +50,15 @@ namespace OpenRCT2::Drawing
             IMPORT_MODE mode = IMPORT_MODE::DEFAULT) const;
 
     private:
+        enum class PaletteIndexType : uint8_t
+        {
+            Normal,
+            PrimaryRemap,
+            SecondaryRemap,
+            TertiaryRemap,
+            Special,
+        };
+
         static std::vector<int32_t> GetPixels(
             const uint8_t* pixels, uint32_t width, uint32_t height, IMPORT_FLAGS flags, IMPORT_MODE mode);
         static std::vector<uint8_t> EncodeRaw(const int32_t* pixels, uint32_t width, uint32_t height);
@@ -59,16 +68,18 @@ namespace OpenRCT2::Drawing
             IMPORT_MODE mode, int16_t* rgbaSrc, int32_t x, int32_t y, int32_t width, int32_t height);
         static int32_t GetPaletteIndex(const GamePalette& palette, int16_t* colour);
         static bool IsTransparentPixel(const int16_t* colour);
+        static bool IsInPalette(const GamePalette& palette, int16_t* colour);
         static bool IsChangablePixel(int32_t paletteIndex);
+        static PaletteIndexType GetPaletteIndexType(int32_t paletteIndex);
         static int32_t GetClosestPaletteIndex(const GamePalette& palette, const int16_t* colour);
     };
 } // namespace OpenRCT2::Drawing
 
 constexpr const GamePalette StandardPalette = { {
-    // 0 (unused)
+    // 0 (Unused/Transparent)
     { 0, 0, 0, 255 },
 
-    // 1 - 9 (misc. e.g. font and water)
+    // 1 - 9 (Misc. e.g. font, water, chain lift)
     { 1, 1, 1, 255 },
     { 2, 2, 2, 255 },
     { 3, 3, 3, 255 },
@@ -79,7 +90,7 @@ constexpr const GamePalette StandardPalette = { {
     { 8, 8, 8, 255 },
     { 9, 9, 9, 255 },
 
-    //
+    // 10 - 21 (Grey)
     { 35, 35, 23, 255 },
     { 51, 51, 35, 255 },
     { 67, 67, 47, 255 },
@@ -92,6 +103,8 @@ constexpr const GamePalette StandardPalette = { {
     { 195, 195, 183, 255 },
     { 219, 219, 211, 255 },
     { 243, 243, 239, 255 },
+
+    // 22 - 33 (Olive)
     { 0, 47, 51, 255 },
     { 0, 59, 63, 255 },
     { 11, 75, 79, 255 },
@@ -104,6 +117,8 @@ constexpr const GamePalette StandardPalette = { {
     { 115, 191, 187, 255 },
     { 139, 207, 203, 255 },
     { 163, 227, 223, 255 },
+
+    // 34 - 45 (Light Brown)
     { 7, 43, 67, 255 },
     { 11, 59, 87, 255 },
     { 23, 75, 111, 255 },
@@ -116,6 +131,8 @@ constexpr const GamePalette StandardPalette = { {
     { 135, 199, 219, 255 },
     { 163, 219, 231, 255 },
     { 195, 239, 247, 255 },
+
+    // 46 - 57 (Yellow, also used for tertiary remap)
     { 0, 27, 71, 255 },
     { 0, 43, 95, 255 },
     { 0, 63, 119, 255 },
@@ -128,6 +145,8 @@ constexpr const GamePalette StandardPalette = { {
     { 95, 243, 255, 255 },
     { 143, 251, 255, 255 },
     { 195, 255, 255, 255 },
+
+    // 58 - 69 (Indian Red)
     { 0, 0, 35, 255 },
     { 0, 0, 79, 255 },
     { 7, 7, 95, 255 },
@@ -140,6 +159,8 @@ constexpr const GamePalette StandardPalette = { {
     { 127, 127, 215, 255 },
     { 159, 159, 235, 255 },
     { 191, 191, 255, 255 },
+
+    // 70 - 81 (Grass Green)
     { 19, 51, 27, 255 },
     { 23, 63, 35, 255 },
     { 31, 79, 47, 255 },
@@ -152,6 +173,8 @@ constexpr const GamePalette StandardPalette = { {
     { 83, 187, 147, 255 },
     { 95, 203, 163, 255 },
     { 103, 219, 183, 255 },
+
+    // 82 - 93 (Olive Green)
     { 27, 55, 31, 255 },
     { 35, 71, 47, 255 },
     { 43, 83, 59, 255 },
@@ -164,6 +187,8 @@ constexpr const GamePalette StandardPalette = { {
     { 147, 219, 195, 255 },
     { 167, 231, 207, 255 },
     { 191, 247, 223, 255 },
+
+    // 94 - 105 (Green)
     { 0, 63, 15, 255 },
     { 0, 83, 19, 255 },
     { 0, 103, 23, 255 },
@@ -176,6 +201,8 @@ constexpr const GamePalette StandardPalette = { {
     { 115, 223, 139, 255 },
     { 143, 239, 163, 255 },
     { 179, 255, 195, 255 },
+
+    // 106 - 117 (Tan)
     { 19, 43, 79, 255 },
     { 27, 55, 99, 255 },
     { 43, 71, 119, 255 },
@@ -188,6 +215,8 @@ constexpr const GamePalette StandardPalette = { {
     { 151, 191, 239, 255 },
     { 171, 207, 247, 255 },
     { 195, 227, 255, 255 },
+
+    // 118 - 129 (Indigo)
     { 55, 19, 15, 255 },
     { 87, 43, 39, 255 },
     { 103, 55, 51, 255 },
@@ -200,6 +229,8 @@ constexpr const GamePalette StandardPalette = { {
     { 223, 183, 183, 255 },
     { 239, 211, 211, 255 },
     { 255, 239, 239, 255 },
+
+    // 130 - 141 (Blue)
     { 111, 27, 0, 255 },
     { 151, 39, 0, 255 },
     { 167, 51, 7, 255 },
@@ -212,6 +243,8 @@ constexpr const GamePalette StandardPalette = { {
     { 243, 211, 143, 255 },
     { 251, 231, 175, 255 },
     { 255, 247, 215, 255 },
+
+    // 142 - 153 (Sea Green)
     { 15, 43, 11, 255 },
     { 23, 55, 15, 255 },
     { 31, 71, 23, 255 },
@@ -224,6 +257,8 @@ constexpr const GamePalette StandardPalette = { {
     { 167, 199, 147, 255 },
     { 195, 219, 175, 255 },
     { 223, 243, 207, 255 },
+
+    // 154 - 165 (Purple)
     { 95, 0, 63, 255 },
     { 115, 7, 75, 255 },
     { 127, 15, 83, 255 },
@@ -236,6 +271,8 @@ constexpr const GamePalette StandardPalette = { {
     { 231, 155, 191, 255 },
     { 243, 195, 215, 255 },
     { 255, 235, 243, 255 },
+
+    // 166 - 177 (Red)
     { 0, 0, 63, 255 },
     { 0, 0, 87, 255 },
     { 0, 0, 115, 255 },
@@ -248,6 +285,8 @@ constexpr const GamePalette StandardPalette = { {
     { 115, 123, 255, 255 },
     { 163, 171, 255, 255 },
     { 215, 219, 255, 255 },
+
+    // 178 - 189 (Orange)
     { 0, 39, 79, 255 },
     { 0, 51, 111, 255 },
     { 0, 63, 147, 255 },
@@ -260,6 +299,8 @@ constexpr const GamePalette StandardPalette = { {
     { 107, 183, 255, 255 },
     { 135, 203, 255, 255 },
     { 163, 219, 255, 255 },
+
+    // 190 - 201 (Water Blue)
     { 47, 51, 0, 255 },
     { 55, 63, 0, 255 },
     { 67, 75, 0, 255 },
@@ -273,7 +314,7 @@ constexpr const GamePalette StandardPalette = { {
     { 231, 231, 171, 255 },
     { 255, 255, 207, 255 },
 
-    // 202 - 213 (Secondary remap)
+    // 202 - 213 (Pink, also used for secondary remap)
     { 27, 0, 63, 255 },
     { 51, 0, 103, 255 },
     { 63, 11, 123, 255 },
@@ -301,27 +342,29 @@ constexpr const GamePalette StandardPalette = { {
     { 195, 219, 231, 255 },
     { 223, 243, 255, 255 },
 
-    // 226 (unknown)
+    // 226 (Extra grey)
     { 75, 75, 55, 255 },
 
-    // 227 - 229 (tertiary remap)
+    // 227 - 229 (Extra yellows)
     { 0, 183, 255, 255 },
     { 0, 219, 255, 255 },
     { 0, 255, 255, 255 },
 
-    // 230 - 239 (water)
+    // 230 - 234 (Water waves)
     { 99, 107, 7, 255 },
     { 99, 107, 7, 255 },
     { 135, 143, 39, 255 },
     { 123, 131, 27, 255 },
     { 99, 107, 7, 255 },
+
+    // 235 - 249 (Water sparkles)
     { 151, 155, 55, 255 },
     { 151, 155, 55, 255 },
     { 227, 227, 155, 255 },
     { 203, 203, 115, 255 },
     { 151, 155, 55, 255 },
 
-    // 240 - 242 (chain lift)
+    // 240 - 242 (Extra grey)
     { 91, 91, 67, 255 },
     { 107, 107, 83, 255 },
     { 123, 123, 99, 255 },
@@ -331,7 +374,7 @@ constexpr const GamePalette StandardPalette = { {
     // { 47, 47, 47, 255 },
     // { 47, 71, 87, 255 },
 
-    // 243 to 254 (primary remap)
+    // 243 to 254 (Primary remap)
     { 47, 51, 111, 255 },
     { 47, 55, 131, 255 },
     { 51, 63, 151, 255 },
@@ -345,6 +388,6 @@ constexpr const GamePalette StandardPalette = { {
     { 63, 183, 255, 255 },
     { 75, 207, 255, 255 },
 
-    // 255 (unused?)
-    { 0, 0, 0, 255 },
+    // 255 (Used in a small number of cases for pure white)
+    { 255, 255, 255, 255 },
 } };