Why do some enlisted sailors have blue piping on the cuffs and collar of their white uniforms?

Well Lt Col Coe, since none of our naval buddies want to jump in and satisfy your curiosity, adding the piping to the whites was a change and they have until 2021 to comply. I wondered the same thing because I swear my Dad had the piping on his whites during WWII and when I saw the sailors without the piping, I wondered how they got off their boat wearing undress whites. Shows what we old guys know!

I saw it too, and as an old Navy Sea Cadet from the 1960’s, our whited had no piping. Then I went back in the Navy Reserve before I was commissioned in the Air Force and we wore these weird white shits, a hat and black slacks. I didn’t stick around long enough to get a set of the “new” old dress whites without piping. I kind of like the look, as it parallels the dress blue “Cracker Jack” uniform, but remember how hard it was to keep whites clean. I wore whites as my work uniform when I was an enlisted ER and ambulance medic in the Air Force, and they were impossible. When they went to the polyester blend whites, they were impossible to keep from yellowing. Anyway, looking good Navy!

Service Dress versus Service Dress Whites

https://www.public.navy.mil/bupers-npc/support/uniforms/uniformregulations/chapter3/MaleEnlisted/ME_ServiceDress/Pages/EM_ServiceDressWhite.aspx