How do you knit vertical stripes?

How do you change yarn colors when knitting vertical stripes?

When working vertical stripes, you must either carry the colors across the back of the work or use separate balls or bobbins for each stripe. If each stripe has four or fewer stitches, carry the yarns across the back. With more than four, use bobbins and twist the colors around each other on every row.

INTERESTING:  What can be made with embroidery?