On modules where you have to set a/serveral color variables, what would I have to set it to to make it use one of the themes $colors?

Most of the modules that are for 6.5 will default to the theme colors. Can you be more specific please. Maybe I don't understand what you mean. Are you trying to write your own module, or you don't want the module to default to the theme, you want it to be a specific color?