craftgrrl | String bikini tops and dye...

Hi there! I'm posting to request some of the community's proven brilliance and craftiness. =)

I bought a string bikini top online that was supposed to be red with black piping. It is actually red with WHITE piping. I don't particularly want to send it back...what I'd like to do is dye the piping black. Does anyone know of a clean and nice looking way to do this? I ONLY want to dye the white piping, I'd like the suit to stay red.

I was thinking I could try permanent marker and slide tape up next to the piping so that the ink doesn't bleed onto the red material of the bikini. Would perm. marker fade, though? Is there a better way to do it?

A note of importance: I will be swimming in salty ocean water with this suit.

ANY flashes of brilliance are supremely WELCOME. I love the top and it would look soooooo cute if I could just change the piping from white to black.

Thanks! ;)