Personally i wouldnt try to dye the seat backs. It may look OK for the first bit, until it starts scuffing, chipping, etc, not to mention when people start sitting in the back! Tan shows a lot!
If you're gonna re-wrap your seats, maybe you can try and find used tan sport seat backings from a busted set, or even if you find black seats, then the black contrast might not look all tha bad on the tan?
Or you can lose the heated seat option all together, and get yourself a nice orginal set...although the heat option is a nice touch in the winter.
I dunno, just my .02cents.