The basics:
DARK BLUE = ANAL
LIGHT BLUE = ORAL
RED = FISTING
BLACK = HEAVY BDSM
GREEN = GAY4PAY
YELLOW = PISS
BROWN = SCAT
ORANGE = ANYTHING, ANYWHERE, ANYTIME (BUT NOT WITH ANYONE)
GREY = BONDAGE & RESTRICTION
LIGHT PINK = DILDOS
MAGENTA = ARMPITS
GOLD = 3SOME
WHITE = HANDJOBS
When the hanky is worn on the left side it signifies the wearer is a top for this particular fetish, when worn on the right the wearer is a bottom. Worn in the middle (for example around the neck) signifies a versatile. Orange worn on the right would mean that the person doesn't want anything right now and is just cruising.
For more, here is a table:
