You can buy tubes of coloured glass paint now - it goes on cold. It tends to go rather streaky when you try to fill a patch of colour in.
I have seen small enamelled martini glasses this shape, but they tend to have fighting cockerels on them.
Stuart did enamel things like this, but I haven't a clue about this, really.

If it was cold painted by somebody at home - the paint will start coming off in hot water and you'll be left with plain glasses.
