I'm no color theorist, but it's confusing to me why he would think the numbers for the perfect blue have to add up to 255 across all three channels. By that log

I'm no color theorist, but it's confusing to me why he would think the numbers for the perfect blue have to add up to 255 across all three channels. By that logic, wouldn't the perfect color white would be R:85 G:85 B:85 (or #555555)?