How colors (primary and secondary) affect the pass

I am looking at using the primary and secondary colors in my engine, but I am not sure how they combine with it…do they add, modulate, or do something different…or can you even change it? Any help would be nice.

Primary color is set using glColor command. If your texture is set to mult, or modulate, then the texture color will be multiplied by the primary color at that vertex.

Secondary color is an extension I think, and is used for specular highlights.