The biggest difference was clearly visible when they hatched, as the heads are much lighter than any regular pastel I've seen. It looks like it tweaks the pattern a bit, with reduced spotting on the sides, and more blushing than normal) - hard to say that though, with the pastel mutation also tweaking the pattern. Additionally, there's the color. It's different from a regular pastel, but that comparison picture isn't the best for that. I can try to get a better one, but I don't have the best camera in the world. Basically these 2 looked different enough from the other pastels in the clutch for me to believe that there is a possibility of this being a new mutation, and it appears to be working as a type of dominance.