Obviously you wouldn't want to paint really anything in 32* weather, but I've done stuff in about 55-ish and all ok. However, if you are going to do it in cooler temps, I would scuff it up a little bit more than normal.
Like halfoftwo said, as long as it's not freezing you should be ok. I also wouldnt do it if it's extremely humid out. I always tried to do my stuff on a nice sunny day so I could leave it out to bake on good. I've done it in the garage in the high 40's low 50's as well and it was ok.