Unit Skin - Tutorial?

Can anyone show me in steps how to edit the skin on a specific unit and add to widget for a multiplayer map without changing the entire game output?

Like the skin of the units aren't exactly the paint as an team color but the entire unit color like steel and where the team paint colors can be added.

I'm only guessing that the team color setup would be a bright green, but I'm not sure if that's how it is on here too.