Amazing Pastels??

So with many different codoms, you might produce beautiful and bright colored snakes or you could potentially produce darker than normal and not so pretty snakes...

What causes this? Specifically, what would cause this in pastels for example? If you have a bright pastel, what would you want to pair her with in order to keep those bright colors in her offspring?

Genetically speaking, I would just guess that if you have a bright pastel and a dark normal, the pastels you produce might be a little darker just because of the genetics taken from each parent.

I think you're right.
I was going to breed my NERD lemon pastel with a beautiful dark normal, thinking that the darkness would deepen the black on the lemon. I was told that it darkens the thing and it is best to breed light and bright colored snakes with light and bright colored snakes!!