I’d imagine that there’s some water vapor sometimes, but either way the gas that’s coming out is going to be warmer than the surrounding atmosphere so shouldn’t there be some sort of condensation or something that allows for a white puff of visability when you fart outside on a cold day?
You haven’t been here long enough, I guess. We’ve had threads on just this topic in the past, with claims of visibility.
Try dropping your trousers for the experiment.
I tried searching first, but as you can imagine searching for farts around here becomes a rather tedious thing after the first thousand threads. 
I would imagine them not to be quite so moist (under hopeful conditions) as exhaled breaths, due to the larger surface of the lungs.
Searching for “visible” and “farts” gives you this 2002 thread:
http://boards.straightdope.com/sdmb/showthread.php?t=115645&highlight=visible+farts
I think Mr. Moto’s comment is the answer - clothing would dissipate or absorb the vapours. I know that when I’ve been out walking my dog in sub-zero temperature and she’s assumed the position, I’ve seen little puffs of vapour.
I know Barbra Streisand recorded a song with the same title as this thread, but I can’t find it on Itunes. Can someone help?
Because it was Bette Midler.
I can’t see them in any kind of weather. I just can’t bend that far.
Fart clouds are not white. They’re green, … in more ways than one.
I thought it was a movie with Jane Fonda.
You *can * see them. I have both produced and witnessed visible cold weather farts.
There are plenty of them walking about around here, any weather!
I can see my dog’s fart puffs, so as mentioned before, it must be the clothing.