this is a great question. i just aquired a large neon green nepthea colony, which was very green at the lfs, and moved it into my tank (400w halide w/ actinics. 60g cube) and have not seen the color come back yet, its been in the tank for about 3 weeks now. so i am giving it time to regain the color. i am noticing a hint of green returning on the branches, but i am still waiting to see.