We had a similar experience when painting our kitchen. We wanted to paint it blue and yellow. Crazy color scheme I know. But, coming to the disaster, my wife painted dark blue where we had intended yellow. This was after scraping, cleaning, sanding, applying putty, sanding again, primer-ing, sanding and where the final two coats of glossy yellow should have gone we painted dark blue. . I was worried that the blue would be too strong and be seen through the yellow paint. We decided to try it out so just sanded it and scruffed it up a bit and painted it yellow on top. Second coat covered all the blue. An extra coat of yellow gave the wall a beautiful finish. Phew.
I've found in many cases that the lighter colors will cover better than darker ones. I think it depends on what base is used to mix the color with. Extra deep base mixtures don't seem to cover worth squat.
"Where all think alike, no one is thinking very much"