To change colors at the end of a dc row: yarn over, insert hook into stitch. Pull up a loop, yarn over, pull loop through first 2 loops on hook. Yarn over with the new color and pull through the remaining two loops on your hook.

Then chain 3 and continue the next row of dc using the new color.

To switch color in the middle of a row, follow the same procedure. Above, the pink yarn is being stranded behind two white stitches. This creates a loop of pink yarn on the wrong side of the work, so this technique is best where the wrong side will not be visible, such as in a pillow cover.