That's what I thought you meant, though it's not generally referred to as seamless. You mean you don't want the color changes to show. On a 2x2 rib scarf, the other color shows on the purl stitches, but not the knit stitches. It might not be so noticeable after a few more inches and the ribbing pulls in a little. Unless there's some kind of slip stitch, I'm not sure how to avoid it, sorry. A 1x1 rib is a tighter rib and it wouldn't be as obvious.