- Added a check to Dehacked code which tries to set the blend color.

It must set it to 0 if the alpha is 0 to avoid problems with special
  colormap detection.
- Changed SPECIALCOLORMAP_MASK again so that it does not interfere with
  any valid setting. It must use a value with a 0-alpha because these
  are guaranteed not to be produced by the DECORATE code elsewhere.
- Fixed precision issues with AddFixedColormap's search for identical colormaps.
- Added custom colormap support to texture composition code.
- Fixed initialization of FSpecialColormap::GrayscaleToColor. This is not
  a mapping from the palette but from a [0,255] grayscale ramp and used to
  apply colormaps to true color images for texture composition.

SVN r1867 (trunk)

src/d_dehacked.cpp

@@ -1793,7 +1793,7 @@ static int PatchMisc (int dummy)
 					{
 						Printf ("Bad powerup color description \"%s\" for %s\n", Line2, Line1);
 					}
-					else
+					else if (a > 0)
 					{
 						static_cast<APowerup *>(GetDefaultByType (types[i]))->BlendColor = PalEntry(
 							BYTE(clamp(a,0.f,1.f)*255.f),
@@ -1801,6 +1801,10 @@ static int PatchMisc (int dummy)
 							clamp(g,0,255),
 							clamp(b,0,255));
 					}
+					else
+					{
+						static_cast<APowerup *>(GetDefaultByType (types[i]))->BlendColor = 0;
+					}
 				}
 			}
 			else