I think the eye color stays the way it is now, or at least very close. I don't think there's any specific strain(s) associated with eye color, only shell patterns. Certain recessive traits can be bred for in selected lines (that stands for any organism), but I doubt that eye color would be a characteristic of interest to breeders. The point being that recessive traits aren't restricted to certain turtle bloodlines, so even if the seller had an answer for you, it probably wouldn't generalize to the general RES breeding population.
At least, that's my understanding of how it works...However, at the end of the day,

.