Ah, my first post on this forum........can't hide in the bushes any longer.
I first visited Zion last February. In my opinion, it's a fantastic time to visit for a couple of reasons. First, if you're lucky, you might get to see a little snow cover in the canyon. In early or late light, the combination of the snow and the reds and yellows is amazing. Second, it isn't really very cold (well, being out before sunrise can be a little chilly) - the days warm up nicely if the sun is out. And third, the crowds are way down. You're also there at a time of year when you can drive freely into the canyon (the shuttles don't run until late March or April).
I agree with the others - going to Utah and not visiting Zion and Bryce would be a huge mistake. Take the time and visit these truly wonderful (and very photogenic) places. You'll never regret it.