White Collar or Blue Collar?

How is it determined if one is white collar or blue collar?
If it’s by the amount of money one makes, then an airline pilot would be white collar but a bus driver would be blue collar. But in a broad sense, they do the same thing.
If it’s determined by the amount of education typically required for a job, then a self made multimillionaire who runs several corporations could be white collar or blue collar.
If it’s determined by whether or not one gets dirty on the job, then a surgeon is blue collar, but a data entry clerk is white collar.

What are the rules for this?

Typically, if you work indoors you’re white collar and if you work outdoors (or indoors as a plumber or furnace repairman or something) you’re blue collar. Blue collar jobs are more physical.