Modelling armor, need help

Heres the scenario.

I am making a game model character fully armored and theres different segments to the armor. Basically each part is seperate from one another. Upper arms are seperate from the forearms, thigh’s are seperate from the knee’s which are then divided at the shins, etc.
My question is, when each indivisual piece is complete, how do I join the parts? Because thats the only way I can get the results I want to make each part a different color. I know theres also UV mapping, but I really want to get this character a specific way.

Thanks.

ctrl+j to join

Thanks man