All colors in Drawing have four 8-bit components: red, green, blue and alpha. Alpha provides a transparency for the color (OpenGL graphics only). Alpha equal to 255 means opaque color, 0 - full transparency. Also, the structure describing a color (IGVectColorEx) has a field defining a color source. If this field is equal to IG_VECT_ATTR_SOURCE_ACTUAL then the red, green blue and alpha are used. In case of IG_VECT_ATTR_SOURCE_BLOCK the actual color is obtained from the including block. IG_VECT_ATTR_SOURCE_LAYER prescribes to use a layer color.