I hate to be that guy and correct me if I'm completely wrong and out of line - BUT if youre talking about the words 'white knuckled' or having 'white knuckles' its not literally describing the mc's skin tone - it's a common term used to describe displaying or characterized by extreme excitement or fear. I think it's called 'white' because when you clench your fist hard enough, you can actually see the knuckle bone. But yeah, in interactive fiction with no set description I think these are phrases that you should probably be wary of when youre writing, like the phrase 'turning red' when describing a character blushing or 'turning blue' if a characters cold