Texture Components
Not every texture requires full color.  Some textures need only vary the existing color or
transparency of a surface, as in partially transparent clouds or water surfaces.  SkyWriter
supports textures of different types as detailed below: Modulation and Decals

Each texture can be treated in two ways when being applied to a polygon.  When operating as a
decal, the color of the texture replaces whatever color is already inherent on the polygon.
When performing modulation, the texture, is blended with the color and surface properties of
the surface and thus will appear differently on surfaces of different color and character.