Arty advice need - coloring/painting glass

Well, I hope one or two of you fine-arts skilled folks can offer me some suggestions. I am working on an art project (I know, most strange! But it's a Feri thing, so of course!).

I have a round crystal (with raised random-y lines, to make things yet more challenging) oil lamp that I want to 'paint'. I'd kinda like the color effects to be fairly sheer, but will go for deep if that's more doable. I'm hoping to draw some fairly simple designs on it, in about half a dozen colors.

I can't draw, let us be clear. So using paint makes me even more nervous. However... I want this to be as fun as it can. Is there a type of marker I can use? If not, what type of paint?

Might be a nice background project at Costume-Con, though I'm leaning heavily towards the hot tub and whatever sun appears. :-)

Thanks guys!