texture color changer

[fascinate4]

Hello, guys. I have one question.

I making a model and i almost done, but i want make a texture, which a user can change color of this texture in gmod (in player model section) , like physgun color changer or some standart half-life 2 playermodels.

How can i make this texture? I tried to google it, but i cant find it, cause i dont know how this procedure is named :)

I hope i was clearly written. Sorry for my bad english.