Haha yeah I know they're not all blue and red. I was just thinking about those two in particular.. I'm just about to get a blue and a red JAQK deck and was interested in what colour people generally prefer between red and blue.
I like both colors, but what I do when I pick a deck is alternate since the last deck, for example if my last deck was a blue back, i will pick the red back. For me, it's like I discover a new deck since I've been only using one color at a time, it's a great feeling.
(Hope you understand what I mean, I don't really speak english...)
I use red-backed Bicycles if I want to use a marked deck, because a red sharpie blends in PERFECTLY with a red back, but not so much blue sharpie on a blue back. However, if I just want a regular deck that isn't marked I will use blue. it sets a calmer mood, and like Pav said, it's easier on the eyes.
I love the blue bicycle cards because they are more appealing to the eyes but recently I've been using red cards because it's easier to see the signature if they sign both sides and most gimmicks like regeneration are red backed.