Ken is right. The urate should be a nice white color and no orange in it. Looking at their eyes is also an indicator. If the eyes look at all saggy or sunken this could indicate dehydration. It depends on what species though. This is much easier to see in pathers though because theyre eyes are much larger and bulbous compared to some other species, especially veileds. So bottom line, check the urate and if its orangish in color, some more misting during the day is in order.
I rarely see mine drink. Especially my male panther. Like they said check his urates and if you are giving him enough water via misting and dripper and he is healthy he should be drinking.
Yeah, that should be good. No more than about 25% yellowish. Of course, sometimes it's going to vary. Don't totally freak out if you get one poop that's mostly yellow, but if they's a few in a row, it could indicate the beginning of dehydration.