I'll keep in mind with the shades, and yeah, it's a series of horizontal mineshafts. Thing in the upper right is an elevator, and the diamond shapes are lights embedded into the walls of the elevator shaft.

And yeah, I could probably stand to smooth out the lights a bit. If this get's rejected, I've got a good starting place, I suppose. :p

 

I'd say four shades max for the light/dark thing. I'm still not sure what all that is, it looks like a bunch of tunnels? I can see that in the upper left corner, but the rest confuses me, especially the diamond shapes on the right side. Light isn't cast in geometric shapes like that. You'll get better with practice though.

Yeah, the size is a definite issue that I'll be more careful with later on, and as for fewer shades, I hadn't actually noticed that, but I may have went a bit overboard with the amount of white in it.

It's really hard to tell what I'm looking at. It would benefit from fewer colors as well. great effort though!