I would have thought that you could put a sepia toned cover picture there without the shot glasses clashing too badly - so long as the image had a strong composition and enough contrast in it to compete and draw the eye.

Otherwise, I would go for something in greyscale, but tinted with one of the colours in the shot glasses.

I find overly loud colours on cover artwork to be quite offputting myself (I'm a cover snob - don't get me started on the torsos!)