Thanks, Blazefire! Now that I see it all tiled together in one big wall like that, it looks pretty good.
I don't think I'll be using those yellow diamonds with the brown ones, as it doesn't make it look much like tree bark, but I'll definitely try out that yellow palette for something else I'm planning; it's a nice, bright set of colors. I'll definitely try to throw something else in there to shake up that pattern -- maybe brighter/darker walls in the middle for added dimension, or I could even throw some plants or leaves in there to make it look more lively.
Thank you for the feedback, it helped to give me some good ideas!