At the time of the Vera Cruz occupation, the sailors mostly wore undress whites but due to the latest uniform regulations (1913 regs, I think) they had a smaller rounded collar, instead of the squared off flap at the back of the collar. Only the undress white uniform was affected by this change, and in just a few years it was changed back. Photos from Vera Cruz show a mix with mostly the small collar, but a few of the old style.