....and marriage it would seem.....
"Married in white, you have chosen right.
Married in green, ashamed to be seen.
Married in grey, you'll go far away.
Married in red, you'll wish yourself dead.
Married in blue, your love will be true.
Married in yellow, You're ashamed of your fellow.
Married in black, you'll wish yourself back.
Married in pink, your spirits will sink.
Married in brown, you'll live out of town.
Married in pearl and you'll live in a whirl."
Not sure why though, in the Middle Ages, green represented evil or demonic beings (including dragons) and sometimes love. Maybe from there.