I think that the Sex Bracelet rumor that surfaced about Jelly Bracelets and Rubber Bracelets is totally fake and was simply the media blowing up parental fears for no good reason. It has been discredited in many places. However, if you must know the supposed "code", this is what many were saying the various colors represented:

black: sex
blue: oral
red: lap dance
purple: holding hands
brown: toss my salad
pink: flash
clear: whatever
white: wildcard
green: outdoor
gold: makeout
glow in the dark: using toys
orange: just kissing
yellow: hug
gray: anal sex
tan: necking
pinkish purple: masturbating for the person
silver: fisting