Likewise, I have the same trouble with my other shop (fabric) and every time I thought I had the color balance absolutely perfect in Photo Paint, the reds and purples would go wonky as soon as I uploaded it, and it still drives me crazy! Even when I laid the fabric flat on the scanner, it seemed to do the same thing. I'd love to know if anyone uploads to different venues, and whether those venues have the same skewing effect on reds and purples, or if it's just something particular to Etsy.
When taking pictures, I found that having complimentary colors together in the same shot somehow made it less bad, but it still wasn't right.