Sounds as if there would be ample grounds for misunderstanding there, if dying your petticoats red could mean either that:
1.You were spoken for, and true to your absent lover, or
2. You were anybody's for the price of a drink.

Must have led to some interesting complications!

But I think there's an in-between explanation too. In the Lichtbob's Lassie, and also the similar Leaboys' Lassie, dying the petticoats red and having them faced with yellow does sound undeniably brash, but the girl is only interested in one man. I took it to mean that the she was going off following the soldiers/ leaboys, and had to accept the somewhat shameful status and dress code of a "camp follower" in order to be with the one she loved.

Marje