Watch color replacement

Sure! While you cannot request an exchange or free replacement, you can purchase a different color/band here.

If you purchased your watch from an Apple Retail Store, Apple Online or an Authorized Apple Reseller, you do have the 14 day grace period to return as long as you have all the parts and there's no damage. If purchased from a non-Authorized Apple Reseller, you can reach out to them to see about exchange/return policy.

If you do end up purchasing an additional band(s):

Change your Apple Watch band

You can buy online, chat, or call (800) MY–APPLE (800–692–7753), 7 days a week from 7:00 a.m. to 11:00 p.m. Central time.

The watch itself or band?

You have 14 days from purchased date to exchange.