Is my wife obligated to wear underwear during the 7 clean days? If she does, it must be white, but is it considered cheating if she doesn’t wear at all?
Yes, she is obligated to wear underwear during the 7 clean days, and it must be white. The reason is because it has to be clear that she didn’t see anything during those days, and if she isn’t wearing anything, or something clored then she isn’t clear that she didn’t see during that period.
Shulchan Aruch Y:D 196-3