I am guilty of letting my son roam topless some days now. Sometimes, I even let him take a nap in the afternoon with no clothes on, with the fan directed to him. It's just so hot and he also hates putting a shirt on.
I just thank goodness we're not living in metal buildings just yet, otherwise we'd all be getting fried alive in this heat.
I just bank on the fact that colds are brought about by viruses, but the old wives' tales refuse to stop ringing in my ears. Even when I've developed a habit of bathing him at night, I also still quietly fear colds while watching him play in his tub.
One thing that I feel has worked for us for real though is sock-wearing for him at night, when we have the A/C on. So far, colds haven't been plaguing him as much.