It is pretty noticeable. I mean I pick them up and hold them upside down to look. lol They don't appreciate it much, but I try to do it fairly quickly. So I don't stress them out even more. Stress is a known cause of pasty bottoms.
How many chicks do you have? Have you seen any evidence of it yet? Or are you just being cautious?
With only 4, you will have no trouble checking their bottoms a few times a day. As long as they are eating and drinking and playing... you should be fine. I've read that having a brooder too warm can also contribute to stress which in turn leads to pasty bottoms. Vitamins and electrolytes are helpful for sure. I have 32 chicks at different ages and I've only had trouble with pasty bottom with 2 or 3. And it only lasted a couple days.