Those windows colors are mainly used by children (like somehow water colors) to be creative. The mass after dry is about a few millimeters thick (depending on how thick you put on the color) between 2-3 millimeters I suppose. You can paint motives at the window so that the sun shining thru makes the colors shine more brightly. There is also a transparent color available. Depending on the type of colors you used, your masterpiece can be stripped of quite easily if not remaining to long at the window glas (and the sun not burned it at the glass -- in this case it is a quite annoying task to remove hardened and not anymore flexible picture from the glas).
