Blastos or brains come in a variety of colors and red looks good on them. They are low light corals and should do well in your tank. The Purple Brush Gorgonian is a photosynthetic variety of gorg but not high light demanding. Although their polyps are brown their outter skin is bright purple and really neat looking. Also Zoa's come in all types of colors, I have a purple and blue cluster, not really sure the specific name. Orange short tenticle plate coral is another nice looking coral. As far as yellow goes other than a deep sea non photosynthetic gorg I am at a loss. Maybe yellow star polyps but I can think of any others for your lighting. Hope this helps