Leopard geckos' patterns change a lot as they mature. For example, super hypos are banded or striped or jungle or have the leucistic juvinile patterns as hatchlings. They eventually loose all opr most of their spots by the time they're adults and at that point, they are considered hypos.
Their colors can change in much the same way. A baby can hatch out yellow or orange or white (snow) but turn out to be completely different as an adult.
Someone once asked Ron Tremper if he could tell if a hatchling that looked yellow as a baby would keep the yellow as an adult. It was merely an OBSERVATION NOT A DEFINITION that the babies didn't have spots on their legs TENDED to keep their yellow as adults.
People over time who either could not read or had heard it from someone just as illiterate have passed it on as a definition of high yellow.
I can tell you just from my own experience and probably everyone else here that has owned a leopard gecko for any legnth of time, that this observation is only correct some of the time.
Basically, if it looks yellow as an adult, it's high yellow. Have you read "The Emperor's New Clothes"? Don't let people try to convince you that you don't see what you do see or you will end up standing on the side of the road looking foolish!