I've heard that some whitewalls just yellow but if you use a light coat of tire paint on them it will keep them white. Here is some offered on ebay. I have not used it, would be worth a try.
http://www.ebay.com/itm/WHITE-WALL-T...a2e9a4&vxp=mtr
By the way...I like whitewalls, I am just not willing for all the work to keep them looking nice!