You can use the RGB components by first masking the blendmap with a texture factor to remove all other colors, use dotproduct3 as the colorop to remove coloring and multiply it with the tiled texture stage. Quick example:

TextureFactor = 0x00FF0000; //Mask for red
ColorOp[0] = DotProduct3;
ColorArg2[0] = Texture;
ColorArg1[0] = TFactor;
////////////////////////////////////////////
TextureTransformFlags[1] = Count2;
TextureTransform[1]= mul(matTerrainTexSize, Skin_Size2);
texcoordindex[1]=1;
ColorOp[1] = Modulate;
ColorArg1[1] = Texture;
ColorArg2[1] = Current;


-Rhuarc