Stock Theme
All beta sites look alike now, so clearly the stock theme isn't going to help disambiguate among them just like the current beta theme doesn't. But could we avoid the stock theme having the same exact colors as non-stock sites? Meta.SE and Super User should have theming that says clearly "not the same as those". Going forward, one of the benefits of "graduation" (or whatever concept replaces it) is that you get to move away from the default; this combination makes it look like these two sites have regressed to that default.