As with any pastel, reguardless of the line, they are going to brown out to some degree as they age. Your best bet is to just shop around, find the highest quality, brightest babies and hope for the best. Seeing pics of parents might help too.

For comparison to the above pics, here is our Graziani line pastel. He is a '10 and around the 400g mark. He has retained his color nicely and his blushing has gotten better.