Pastel isn't an inhertible trait. Actually they are produced by high incubation temps. Many are incubated at such extremes you see various shell deformaties. I've even seen them with no eyes! Not sure if there has been any improvements but its seems you only find fresh hatchlings in any numbers. Rarely can one find any well started or larger turtles. I don't personally take interest in a mutation that is nothing more than visually appealing, for breeding they are nothing more than normal RES.
Xavier