Alright, I guess the only way to get a computer and a player to control units of the same color is to actually make those players the same color. That will take care of the minimap, but it will make distinguishing allies very difficult. DTBK brought up an exceedingly obvious point. I guess my sneaky method won't really work. I guess I could force allied status to make you have to pick your targets, but then a unit wouldn't auto attack when being attacked either.
For the purposes of Cops and Robbers, I guess I can just make them all the same color. Then robbers would have to maintain their distance from the cops to avoid being found. I'm not sure how that sort of gameplay would work out though.

I want units from player1 to be given to player2, but the units color must still be the same. Is that possible without making the units "rescuable"?

Nope, sorry