RES often get darker as they age, so you might be able to find a pair of really dark specimens, but the offspring might well look regular until they're adult. I've seen some photos of wild ones and they look amazing though
Best,
Paul
Out of stock at the moment but, they are here, and pricey:
http://www.theturtlesource.com/i.asp?id=100200375&p=Lemon-Yellow-Albino-Red-Eared-Sliders