As long as it's nice art, I don't really mind. Generally, I like B+W art better because it photocopies better, making it easier to make my own 'You See This!!' sheets and the occassional bit of character art if something in the book looks very much like a character I'm playing; I can copy it, snip it, and put it in the charatcer folder.
I am utterly ignorant about the actual printing costs or going rate for color vs. b+w art. If it actually make a significant difference in price for the book, go with B+W. For instance, if Book XX with normal paper and B+W art costs $20.00 vs. slick paper and color art throughout at $35.00, I'd prefer the $20.00 version, myself.