If you take your regular chestnut and give it a cream gene, you'd get a palomino. If you gave it two cream genes you'd get a cremello. So it's kind of like an extra diluted palomino. FYI- If you had bay and gave it a cream gene you'd get a buckskin. If you gave it two you'd get a perlino. It's a bit more complicated then that', but that's the general idea.
I've also heard but don't have proof that light colored horses suffer from fly's bothering them more. When I heard that it explained to me why Toby is always covered in flies while my other horses are not. And looking at this Cremello's picture, I was not surprised to see him covered in flies too. :(