IMHO, the new blackish action/submit buttons don't fit into the overall design of the page at all. For me they feel like a fist on the eye (as we say in the German language room). They have this very dark, monochrome, 3Dish look while the rest of the site is light, colourful and exceptionally non-3D. Is there a good reason behind this? It seems quite like a step back from what we had before, from a graphic design point of view.
How about to select a color that is the same harmony wheel with the rest ? I Check the link color is the opposite of the main SO color, so the button can be ether the same as the link, or the near darkest one as:
and how is look with many buttons together:
and one more on the link colors:
This is just an idea, do not take it as suggestion or anything. Totally personal, just "play" with the design.