Kevin Varney, who unfortunately passed a couple of years ago, used to use India Ink on Purple Heart.
That used to come out most beautiful for him. Ya wanna be using rubber gloves when you use India, cause even Acetone doesn't take that off. It wears off by itself.
In a couple of years, maybe, if yer lucky.
I swear by the pictures that he had posted, one couldn't see the difference. I used India Ink on Cork but apparently, as Ryan mentioned, it doesn't take to neoprene. The actual Cork dyed well tho.