Yes, you can feed mushroom or yumas with tiny bit of shrimp but not practical unless that yumas and mushroom is one of a kind, ie Pink Mushroom, Blue Yumas... They can survive well with relying on lighting alone...
Zoas definitely dun need "feeding" or at least not with shrimps..
Blue light will normally bring out the color of the zoas and mushroom more... not as viewing it in blue light... White light will help it to grow and as while as maintain the coloration, becos normally white light have all spectrum color...