Generally speaking there are always gut noises, but that doesn't mean 24/7 -- in between there are quiet times.
Of course a horse's legs can be too cold -- so can yours, but it's highly improbable. Unless there is a health issue, in which case there would other symptoms as well.
I have never even attempted to measure the temperature of a horse's legs or hooves. If I don't know the horse, I will run my hands over the whole horse looking for "hot" spots. Generally, I find a horse is warmer than I am, but standing in sun or shade can affect that greatly especially on very dark or very light coloured horses. For hooves, you can often pick out a potential problem by comparing one to the other three. But if there is something in all four -- well... but again, likely in that kind of scenario that there would be other signs.
For your own horse, the best method is to measure your horses heart and breathing rates over several days to establish a baseline. Then if something is out of sorts, you have something to check against. For general "I know my horse" kind of going over, I make a point of running my hands over my horses regularly even if I don't have time to groom (plus hands will tell me things that brushes won't). I look at their eyes, general demeanour, headset, earset, body language.
Sorry I'm not very specific, but maybe this helps you a bit?