Yes for green although not as heavily used the way blue/red mono teams are, but still needed. Not for yellow/purple.
I went ahead and made the other colors just because I wanted a base of 5 for each element, and they could be used in tournaments, I agree with @Guvnor about the versatility.
My maxed greens are Isshtak, Mnesseus, 2x Berden, Hisan, reg and costume Brienne. I also maxed Belith. And for straight up game fun, I maxed 5 muggy’s and use them as a mono team #DoYouEvenMuggyBro 
Purple is 2 Balthazar, Chochin, Gill-Ra, and Tyrum (only because he was my first maxed 3), because they aren’t used in challenge events I never maxed any of the others like Bat/Bjorn although I have them.
Yellow is Melia, 2 Pixies, Bane, Arman and Kailani.