Edited to a better link.
I've looked into this before. There are several ways of achieving this kind of effect. The first is simply using translucent paints. The second is to use a 'glaze' that has to be fired and forms a permanent bond with the glass.
The second gives less consistent, but more permanent results. And is very, very technically challenging.
I am fairly certainly that the large lines are the lead came, and the smaller black lines are an opaque glaze. So the head and hair, for instance, are a single piece that was probably a peach-colored glass that was then painted with glaze--the hair is a built-up color from the base--fired, and soldered into place. The garment appears to use a different color of glass as the base, with built up shadows, fine lines, and (I think?) a white glaze for highlights.
It's an artform that requires a high degree of technical mastery over multiple different elements. It's a pity that it's so rare to see this kind of work anymore. Then again, I'd never be able to afford it, so...