Hi,
They don't if you look closely enough.
Black pastels have markings around the eyes in the "alien heads" on their sides and can be a bit more orange in the colouration on occasion.
But the main difference, and the reason there is such a difference in price is the super form of the black pastel is a solid coloured snake - the background colour of the BP.
So while an albino black pastel and an albino look similar from a distance an albino super black pastel would be a solid white snake with red eyes and no pattern.
But the more genes in any animal the more it will cost because of the flexibility it gives in breeding so a pastel albino costs way more than a regular albino.
But when bred to another animal 50% of the offspring would not only be het albino but also pastels. Does that make sense?
dr del