How to determine player coloured areas in the TGA/DDT files

Hi,

I'm working on a minor mod I made for myself since I enjoy doing a lot of programming and coding stuff. But currently, I'm facing one problem (there are actually quite a lot but this one is the one that's troubling me the most), that is I do not know how do you define which part of the image shall show the player colour. For example, I'm currently working on a new unit which requires a new texture, but then I don't know how to I tell it where and how the player colour shall be. I'm not sure if I'm in the right place to ask this but hopefully, there'll be some answers here.

Thanks.