There is a Graphics Design stack exchange currently in beta.
Additionally there is a proposed site that seems to fit the desires you have, covering art creation in general. From the proposal:
Proposed Q&A site for artists, painters, drawers, caricaturists,
illustrators, cartoonists, graphic artists, engravers, sculptors, etc.
Basically art techniques and methodologies.
However, I don't know how long these things generally take, but the Art Creation site was proposed nearly a year ago and only has 10% commitment. Seems a long way off from the 100% needed to start beta. I guess it's time to start some promotion of your own if you want to get the site off the ground :)
As far as where the questions should go. I agree with Tetrad that on topic questions should come to us, I just don't think they have the same chance of being answered. Personally, if I had an art question, I would go for the site that's more likely to get the question answered, Graphics Design.
Game Developmentitself seems pretty low-use. I asked one XNA-centric question and received no replies for weeks, where I've seen similar questions answered quickly on
App Hub. My new approach is to post on both sites, assuming the
App Hubone is most likely to "hit" a good response. \$\endgroup\$