Got a lot of feedback from my contest buddies, and I think the advice really paid off! Here he is, new and improved:
The blue was brightened by adding quite a few drops of white with about half as many silver and a single drop of red. The red benefited from a combination of yellow and Bronzed Flesh, though just a very small amount of the latter. Finally, the gold wasn't mixed in a different way, but instead I layered yellow, then silver, and then finally Shining Gold on top.
Thanks to all of the people who gave me advice... now to just paint all the others!