Depending on the type of glass. It can absorb part of you light spectrum and it looks dull. This of course relates to Refractive index. Look at starfire vs ordinary glass

could it be all in our heads...?

by this I mean, we get used to seeing our tanks on a daily basis and we get used to what we see as for color, but then you change the view and it looks tottally different something we dont see that often.

But I think its more on the right track of, the light is hitting the coral right on the top of the colony, and giving it more color and more energy.
I had to test this out, so I just fragged a piece of my green slimer, when i was holding it in the tank and rotated it, it looked like it had much more color.

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).

I don't have a theory but I will say I prefer your stylo head-on 100x. I've always preferred FTS over all the top-down coral pics.

This is why. Corals make pigment to protect from UV rays. Obviously the UV rays are coming from above, so the most pigment will be seen when viewing from that direction. ;)

Light your corals from the side, and they will color up on that side. :lol:

I vote for "light from above". If you inspect your corals and look at the parts where the light doesn't hit it directly (like a shaded side or the base of a branching colony), the colours aren't that great at all. At least that's the case for my corals. They go from amazing from the top, to pretty good/okay on the sides to dull and possibly brown at the bottom (undersides of branches, base of colony, side of coral not getting direct light). Anyway, that's what I notice with my corals.

I would agree that corals are more pigmented where the "sunlight" hits them but a glass interface reduces the amount of light through.

Imagine looking at penny top down through one foot of water. Then imagine looking at the same penny through one foot of glass. The penny under the glass would look dull compared to the water penny.

Interesting logic but I'm not sure who's tank was 12" thick glass or who even has a piece of glass like that lying around to try such an experiment :lol: Glass actually has a refraction index close to water it's about 1.4 compared to 1.3, so given that tanks are generally built with thin glass when compared to the amount of water you're looking through the effects are not that relative. Try looking through glass from top down, which is often done for photography, you won't see a real noticeable difference.

The fact is, like already said, everything looks brighter and more vivid because you're looking parallel to the light source. Our vision is based on how light reflects back to our eyes and parts in direct light look brighter while other parts not in direct light are more shaded and dull. Look around outside as some stationary objects when the sun is low in the morning and when it is high in the afternoon.

So if water has a comparable refractive index as glass then surely then refraction is not the issue here correct? My logic is that the glass just does not allow some of the light through.

Again lets look at the 3/8" glass cover on the face of a metal halide light, it blocks up to 80%? of the UV rays does it not? This to me illustrates clearly that glass has great potential to block light.

Glass can filter UV but this would also be irrelevant since UV is not visible to us and therefore doesn't greatly effect how we see things. Glass will block/absorb light, but so does water which is why light intensity is less with more water depth. You should also note that the glass used in MH fixtures has a coating or specific formula to lower the emissivity which results in the high reflection of UV light, this is not typical with standard glass.

The point is the glass has little to no effect on the topic here. If you could remove the glass from your aquarium you would still see the same effect comparing top to side views (other than a little less green tint from the sides). Acrylic has no tint and the index of refraction is even closer to water and yet these tanks still suffer from side perspective. For this reason I don't see glass as part of the equation, if a variable can be removed without effecting the outcome then it is not part of the problem.