why top downs ?

[BlueAbyss]

I'm thinking also that the angle that the light hits it may affect the color also... when my green palys are in the center of the tank (light from directly above) they look bleached out unless they are on the sandbed (like they are reflecting or 'mirroring' the light). They look vibrant green and pink/purple when they are up on the rockwork near the sides of the tank, so it may have to do with reflection(?) within the coral's tissues also. I just noticed this today when I moved them to fill some space (never noticed the purple tones before).