You're HTML is valid, and thats a good start, but your CSS is not, which can be just as bad (or worse) as invalid HTML.
Things aren't lined up (eg site map and welcome boxes with the red banner).
I have no real beef with the color scheme. Reds and browns typically work very well together, but that bright cyan just doesn't seem to work. Also the dark blue text is hard to read. Try increasing the margins around the light brown boxes to get a better "buffer"...so the text in it doesn't seem so crammed.
Eliminate clutter. For example, the "program notes" section at the bottom. Is that really necessary? It doesn't seem important to me (maybe it is to your viewers...I doubt it, but I don't know for certain)...just take it out.
Have you tested your site in all browsers? I doubt it, because it looks horrible in Netscape. "Program Notes" is horizontally aligned to "site map" There is a random grey bar running across the screen, and I can't even read the text under the "site map"....its just too tiny.
If you can, make your site less image intensive (a strange paradox for an art site, I know) but it takes ages to load on dial up.