I found this great tutorial
Today we’re making a two-color spiral in double crochet. You can use this technique to add more colors, too!
With yarn A make a Magic Circle.
Chain 1, 1 single crochet, 1 half double crochet, 2 double crochet. Pull the loop bigger and remove the hook.
Attach yarn B, chain 1, 1 single crochet, 1 half double crochet, 2 double crochet.
Pull Magic Circle tight.
Continue with B, 2 double crochet into single crochet (A), hold down the loop of yarn A to keep it from getting tangled in the hook …
… and do 2 double crochet into next 3 stitches.
Pull the loop bigger and insert hook into loop of yarn A. Work 2 double crochet into single crochet (B), continue this way to the last stitch of yarn B.
Fasten off yarn A.
With yarn B work 2 double crochet into each of next 8 stitches. Fasten off.
Additional colors can be added at the beginning. Each color is worked in the same way as shown here.