There are really "ugly" pastels out there. You can still tell they are pastels but they are not what I would call great looking.

If you are going to breed, find THE BEST pastel you can and breed it to THE BEST normal you can find.
Also, pics of the parents of the pastel help.
The colors do fade as they age but there is really no way to mistake an adult pastel from an adult normal when you see them together.