It's pretty hard to tell what color the picture really looks like at 51200 on my K-5 because of all the noise, but I didn't notice anything particularly off at 12800 or 25600, Auto NR Off, JPEG or RAW. The chroma noise at 51200 can make the color look somewhat off, but overall the color looks roughly correct on my camera.
You're going to have to post larger pictures from both low and high ISO for us to be able to see what's going on. We can't tell anything from that small photo, because we don't know what that scene looks like at low ISO.
EDIT: Unless you're talking about the yellow band in the middle of that picture. Is it supposed to be more or less white across the whole thing? If so, then no, my camera doesn't do that.
Not that I personally would ever really use 51200, or 25600 for that matter anyway. There's a reason they're "expanded" ISO, and not selectable by default. Unless you have crazy NR skills like JohnBee, they're not really usable.