Those aren't called seams; seams are where you sew two pieces together.
You can do stockinette which is knit one row and purl one row then alternate them, and change yarn color on the knit row. However, a scarf in stockinette will curl up unless you do plain knit sts at the beginning and end of every row. You might try k1, p1 ribbing which looks almost like stockinette. If it's stretched out you do see the color changes, but it usually draws in so much that you don't see them as much as with knitting every row.