Mason, I took a little time messing with the colors (only slightly) and printed a couple off on gloss paper... threw them over a couple books of the same size and threw them on the shelf.
I put a couple pretty bright books and even then the blue seems to hold up. The red could use a little more work.
One thing I notice looking through my bookshelf overall is that it's a lot easier to get some "pop" out of shorter titles, esp with bright text on dark backgrounds. Look at Super System or 7 Card Stud, the relatively short title allows for some big lettering.
Now look at Harrington's... his red cover jumps out, but the title is lost in a mess. Same with Phil Gordon's book. Just an argument against super-long titles in general...
Anyway, lightening the colors is easy, but if I over do it the text will get a little washed out. If you have any last minute pointers based on the photos this is pretty much my last chance to fix it.