All colors in a Drawing have four 8-bit components: red, green, blue, and alpha. Alpha provides transparency for the color. Alpha equal to 255 means fully opaque color; 0 means full transparency.

Also, the structure describing a color (IGVectColorEx) has a field defining the color source.

• If this field is equal to IG_VECT_ATTR_SOURCE_ACTUAL then the red, green, blue, and alpha are used.
• If this field is equal to IG_VECT_ATTR_SOURCE_BLOCK then the actual color is obtained from the including block.
• If this field is equal to IG_VECT_ATTR_SOURCE_LAYER then the actual color is obtained from the layer.