Color mixing just from lights shown-was just the whole question here? See my other LED Light question I posted in another discussion page-that tell what other Disco LED light device that I would want (exactly).
Not sure a cathode-ray tube is classed as a light-emitting diode....
.... Or could it be?
After all, it is fundamentally a thermionic valve whose anode is a set of phosphor grids (red, green, blue), and any such valve does function as a diode.