Stripes in the round can be hard in crochet, because usually you can see the seam when you slip stitch to start a new round.
I think my way of doing it is seamless, and it all has to do with where you start your new color!
To make these leg warmers you will need about 300 yards of worsted weight yarn in two colors, so 150 yards of color A and 150 yards of color B. I used a size 4.5mm crochet hook and I have a 8 inch ankle. There are 3.5 hdc sts an inch for gauge when working hdc in the round. Finished legwarmers is 10 inches long with a circumference of 9 inches, measured without stretch. Will fit a 8-11 inch ankle. My ankle is 8 inches but my calf is 12 and it got a bit tight at the top but it still worked. Increase your starting chain if you ankle is bigger by 4 chains an inch, and decrease by 4 chains an inch if smaller.
Chain 39 sts.
R1: Skip first chain, and do 38 hdc, one in each chain down the row
Join in the round (I sl st into the first hdc)
R2: Chain 1, and do 38 half double crochets all the way around one in each st. Slip stitch into the first stitch, cut yarn.
R3: NEW COLOR! pull up a stitch, and chain one. To make it seamless, make sure to start in new stitch NOT where you sl st in the previous round with your old color. do 38 half double crochets all the way around one in each st. Slip stitch into the first stitch.
R4: Chain 1, and do 38 half double crochets all the way around one in each st. Slip stitch into the first stitch, cut yarn.
Repeat round 3-4 until desired length. I did 14 stripes. If you want more stripes make sure you have more than the recommended 150 yards of yarn. Good luck!