Quick question that may seem silly (hey, I'm still a wet-behind-the-ears, snot-nosed, newbie): How important is the use of bright colors in the design of the cover for an e-book?

I have always been taken with black as a motif, and think it can look really cool if combined correctly with other colors. So I used it as the cover of my report. But my partner (who has more internet marketing experience than I do) said it needed to be changed to reds and whites and yellows and oranges and maybe some blue. He says it will sell better that way.

Is there any prevailing wisdom on this matter?

Thanks!

Ken