diff --git a/src/raster/color.h b/src/raster/color.h
index 63c425ebc..085581136 100644
--- a/src/raster/color.h
+++ b/src/raster/color.h
@@ -29,10 +29,16 @@ namespace raster {
   //////////////////////////////////////////////////////////////////////
   // RGBA
 
-  const int rgba_r_shift = 0;
-  const int rgba_g_shift = 8;
-  const int rgba_b_shift = 16;
-  const int rgba_a_shift = 24;
+  const uint32_t rgba_r_shift = 0;
+  const uint32_t rgba_g_shift = 8;
+  const uint32_t rgba_b_shift = 16;
+  const uint32_t rgba_a_shift = 24;
+
+  const uint32_t rgba_r_mask = 0x000000ff;
+  const uint32_t rgba_g_mask = 0x0000ff00;
+  const uint32_t rgba_b_mask = 0x00ff0000;
+  const uint32_t rgba_rgb_mask = 0x00ffffff;
+  const uint32_t rgba_a_mask = 0xff000000;
 
   inline uint8_t rgba_getr(uint32_t c) {
     return (c >> rgba_r_shift) & 0xff;
@@ -60,8 +66,11 @@ namespace raster {
   //////////////////////////////////////////////////////////////////////
   // Grayscale
 
-  const int graya_v_shift = 0;
-  const int graya_a_shift = 8;
+  const uint16_t graya_v_shift = 0;
+  const uint16_t graya_a_shift = 8;
+
+  const uint16_t graya_v_mask = 0x00ff;
+  const uint16_t graya_a_mask = 0xff00;
 
   inline uint8_t graya_getv(uint16_t c) {
     return (c >> graya_v_shift) & 0xff;
diff --git a/src/raster/rotate.cpp b/src/raster/rotate.cpp
index 4bd93c290..7b5c341a8 100644
--- a/src/raster/rotate.cpp
+++ b/src/raster/rotate.cpp
@@ -188,36 +188,46 @@ protected:
 
 class RgbDelegate : public GenericDelegate<RgbTraits> {
 public:
-  RgbDelegate() {
+  RgbDelegate(color_t mask_color) {
     m_blender = rgba_blenders[BLEND_MODE_NORMAL];
+    m_mask_color = mask_color & rgba_rgb_mask;
   }
 
   void feedLine(Image* spr, int spr_x, int spr_y) {
     ASSERT(m_it != m_end);
 
-    *m_it = m_blender(*m_it, spr->getPixel(spr_x, spr_y), 255);
+    register int c = spr->getPixel(spr_x, spr_y);
+    if ((c & rgba_rgb_mask) != m_mask_color)
+      *m_it = m_blender(*m_it, c, 255);
+
     ++m_it;
   }
 
 private:
   BLEND_COLOR m_blender;
+  color_t m_mask_color;
 };
 
 class GrayscaleDelegate : public GenericDelegate<GrayscaleTraits> {
 public:
-  GrayscaleDelegate() {
+  GrayscaleDelegate(color_t mask_color) {
     m_blender = graya_blenders[BLEND_MODE_NORMAL];
+    m_mask_color = mask_color & graya_v_mask;
   }
 
   void feedLine(Image* spr, int spr_x, int spr_y) {
     ASSERT(m_it != m_end);
 
-    *m_it = m_blender(*m_it, spr->getPixel(spr_x, spr_y), 255);
+    register int c = spr->getPixel(spr_x, spr_y);
+    if ((c & graya_v_mask) != m_mask_color)
+      *m_it = m_blender(*m_it, c, 255);
+
     ++m_it;
   }
 
 private:
   BLEND_COLOR m_blender;
+  color_t m_mask_color;
 };
 
 class IndexedDelegate : public GenericDelegate<IndexedTraits> {
@@ -278,7 +288,7 @@ public:
 template<class Traits, class Delegate>
 static void ase_parallelogram_map(
   Image *bmp, Image *spr, fixed xs[4], fixed ys[4],
-  int sub_pixel_accuracy, Delegate delegate = Delegate())
+  int sub_pixel_accuracy, Delegate delegate)
 {
   /* Index in xs[] and ys[] to topmost point. */
   int top_index;
@@ -685,13 +695,17 @@ static void ase_parallelogram_map_standard(Image *bmp, Image *sprite,
 {
   switch (bmp->getPixelFormat()) {
 
-    case IMAGE_RGB:
-      ase_parallelogram_map<RgbTraits, RgbDelegate>(bmp, sprite, xs, ys, false);
+    case IMAGE_RGB: {
+      RgbDelegate delegate(sprite->getMaskColor());
+      ase_parallelogram_map<RgbTraits, RgbDelegate>(bmp, sprite, xs, ys, false, delegate);
       break;
+    }
 
-    case IMAGE_GRAYSCALE:
-      ase_parallelogram_map<GrayscaleTraits, GrayscaleDelegate>(bmp, sprite, xs, ys, false);
+    case IMAGE_GRAYSCALE: {
+      GrayscaleDelegate delegate(sprite->getMaskColor());
+      ase_parallelogram_map<GrayscaleTraits, GrayscaleDelegate>(bmp, sprite, xs, ys, false, delegate);
       break;
+    }
 
     case IMAGE_INDEXED: {
       IndexedDelegate delegate(sprite->getMaskColor());
@@ -699,9 +713,11 @@ static void ase_parallelogram_map_standard(Image *bmp, Image *sprite,
       break;
     }
 
-    case IMAGE_BITMAP:
-      ase_parallelogram_map<BitmapTraits, BitmapDelegate>(bmp, sprite, xs, ys, false);
+    case IMAGE_BITMAP: {
+      BitmapDelegate delegate;
+      ase_parallelogram_map<BitmapTraits, BitmapDelegate>(bmp, sprite, xs, ys, false, delegate);
       break;
+    }
   }
 }