Not a myth, I'm afraid. Google "lacquer for glass" and you'll find plenty of products available for crafters, so that they can colour glass, mostly for stained glass effect and home decor. These probably won't fool anyone who knows about glass and looks closely.
However, there is a potential for colouring nano-lacquers, such as the clear coatings that are applied to your car bodywork and windscreen. These adhere extremely well, can be applied thinly, and are very durable and scratch-resistant. So long as the mixture is applied to a piece of glass in good nick, and coats both inside and out, it would be virtually invisible and require you to chip or break the item to detect the treatment
New coatings are being developed all the time. Some require curing in a kiln or kitchen oven. Others do not. It might not bother glassies too much, since values are relatively low, but some bottle collectors have collections worth thousands (http://www.bbc.co.uk/programmes/b006mj2y/features/poison
), and they get quite twitchy when the subject comes up