diff --git a/data/shaders/fillrect.frag b/data/shaders/fillrect.frag
index d61e07d719..5f25f15eb7 100644
--- a/data/shaders/fillrect.frag
+++ b/data/shaders/fillrect.frag
@@ -3,9 +3,9 @@
 uniform ivec4 uClip;
 
 uniform int   uFlags;
-uniform vec4  uColour;
+uniform vec4  uColour[2];
 
-flat in ivec2 fPosition;
+in vec2 fPosition;
 
 layout (location = 0) out vec4 oColour;
 
@@ -16,6 +16,14 @@ void main()
     {
         discard;
     }
-    
-    oColour = uColour;
+
+    int posSum = int(fPosition.x) + int(fPosition.y);
+    if ((posSum % 2) == 0)
+    {
+        oColour = uColour[0];
+    }
+    else
+    {
+        oColour = uColour[1];
+    }
 }
diff --git a/data/shaders/fillrect.vert b/data/shaders/fillrect.vert
index 1437b1ff59..997f383fc5 100644
--- a/data/shaders/fillrect.vert
+++ b/data/shaders/fillrect.vert
@@ -4,14 +4,14 @@ uniform ivec2 uScreenSize;
 
 in ivec2 vPosition;
 
-flat out ivec2 fPosition;
+out vec2 fPosition;
 
 void main()
 {
     fPosition = vPosition;
 
     // Transform screen coordinates to viewport
-    vec2 pos = vec2(vPosition);
+    vec2 pos = vPosition;
     pos.x = (pos.x * (2.0 / uScreenSize.x)) - 1.0;
     pos.y = (pos.y * (2.0 / uScreenSize.y)) - 1.0;
     pos.y *= -1;
diff --git a/src/drawing/engines/opengl/FillRectShader.cpp b/src/drawing/engines/opengl/FillRectShader.cpp
index 4eee172f90..20828af765 100644
--- a/src/drawing/engines/opengl/FillRectShader.cpp
+++ b/src/drawing/engines/opengl/FillRectShader.cpp
@@ -45,7 +45,8 @@ void FillRectShader::GetLocations()
     uScreenSize = GetUniformLocation("uScreenSize");
     uClip       = GetUniformLocation("uClip");
     uFlags      = GetUniformLocation("uFlags");
-    uColour     = GetUniformLocation("uColour");
+    uColour[0]  = GetUniformLocation("uColour[0]");
+    uColour[1]  = GetUniformLocation("uColour[1]");
 
     vPosition   = GetAttributeLocation("vPosition");
 }
@@ -65,9 +66,9 @@ void FillRectShader::SetFlags(uint32 flags)
     glUniform1i(uFlags, flags);
 }
 
-void FillRectShader::SetColour(vec4f colour)
+void FillRectShader::SetColour(int index, vec4f colour)
 {
-    glUniform4f(uColour, colour.r, colour.g, colour.b, colour.a);
+    glUniform4f(uColour[index], colour.r, colour.g, colour.b, colour.a);
 }
 
 void FillRectShader::Draw(sint32 left, sint32 top, sint32 right, sint32 bottom)
diff --git a/src/drawing/engines/opengl/FillRectShader.h b/src/drawing/engines/opengl/FillRectShader.h
index 0f82d8a68c..2d99ba6d71 100644
--- a/src/drawing/engines/opengl/FillRectShader.h
+++ b/src/drawing/engines/opengl/FillRectShader.h
@@ -25,7 +25,7 @@ private:
     GLuint uScreenSize;
     GLuint uClip;
     GLuint uFlags;
-    GLuint uColour;
+    GLuint uColour[2];
 
     GLuint vPosition;
 
@@ -39,7 +39,7 @@ public:
     void SetScreenSize(sint32 width, sint32 height);
     void SetClip(sint32 left, sint32 top, sint32 right, sint32 bottom);
     void SetFlags(uint32 flags);
-    void SetColour(vec4f colour);
+    void SetColour(int index, vec4f colour);
 
     void Draw(sint32 left, sint32 top, sint32 right, sint32 bottom);
 
diff --git a/src/drawing/engines/opengl/OpenGLDrawingEngine.cpp b/src/drawing/engines/opengl/OpenGLDrawingEngine.cpp
index d5e5c8fe9d..314d69ab4f 100644
--- a/src/drawing/engines/opengl/OpenGLDrawingEngine.cpp
+++ b/src/drawing/engines/opengl/OpenGLDrawingEngine.cpp
@@ -142,8 +142,8 @@ public:
 
         _drawingContext->Initialise();
 
-        // glEnable(GL_BLEND);
-        // glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+        glEnable(GL_BLEND);
+        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
     }
 
     void Resize(uint32 width, uint32 height) override
@@ -158,6 +158,8 @@ public:
         for (int i = 0; i < 256; i++)
         {
             SDL_Color colour = palette[i];
+            colour.a = 255;
+
             Palette[i] = colour;
             GLPalette[i] = { colour.r / 255.0f,
                              colour.g / 255.0f,
@@ -326,61 +328,20 @@ void OpenGLDrawingContext::Clear(uint32 colour)
 
 void OpenGLDrawingContext::FillRect(uint32 colour, sint32 left, sint32 top, sint32 right, sint32 bottom)
 {
-    vec4f paletteColour = _engine->GLPalette[colour & 0xFF];
+    vec4f paletteColour[2];
+    paletteColour[0] = _engine->GLPalette[(colour >> 0) & 0xFF];
+    paletteColour[1] = paletteColour[0];
+    if (colour & 0x1000000)
+    {
+        paletteColour[1].a = 0;
+    }
 
     _fillRectShader->Use();
     _fillRectShader->SetScreenSize(gScreenWidth, gScreenHeight);
-    _fillRectShader->SetColour(paletteColour);
+    _fillRectShader->SetColour(0, paletteColour[0]);
+    _fillRectShader->SetColour(1, paletteColour[1]);
     _fillRectShader->SetClip(_clipLeft, _clipTop, _clipRight, _clipBottom);
-    _fillRectShader->Draw(left, top, right, bottom);
-
-    return;
-
-    if (left > right)
-    {
-        left ^= right;
-        right ^= left;
-        left ^= right;
-    }
-    if (top > bottom)
-    {
-        top ^= bottom;
-        bottom ^= top;
-        top ^= bottom;
-    }
-
-    left += _offsetX;
-    top += _offsetY;
-    right += _offsetX;
-    bottom += _offsetY;
-
-    left = Math::Max(left, _clipLeft);
-    top = Math::Max(top, _clipTop);
-    right = Math::Min(right, _clipRight);
-    bottom = Math::Min(bottom, _clipBottom);
-
-    if (right < left || bottom < top)
-    {
-        return;
-    }
-
-    glDisable(GL_TEXTURE_2D);
-
-    if (colour & 0x2000000)
-    {
-        glColor4f(paletteColour.r, paletteColour.g, paletteColour.b, 0.4f);
-    }
-    else
-    {
-        glColor3f(paletteColour.r, paletteColour.g, paletteColour.b);
-    }
-
-    glBegin(GL_QUADS);
-        glVertex2i(left,  top);
-        glVertex2i(left,  bottom + 1);
-        glVertex2i(right + 1, bottom + 1);
-        glVertex2i(right + 1, top);
-    glEnd();
+    _fillRectShader->Draw(left, top, right + 1, bottom + 1);
 }
 
 void OpenGLDrawingContext::DrawLine(uint32 colour, sint32 x1, sint32 y1, sint32 x2, sint32 y2)