If you cannot easily remove the green screens, you will need to cut them off with a dremmel type thingymajig.
The only trouble getting rid of these is it can make the illumination a little patchy on some, or you could use green led's ?, these will give a more even light colour and are cheap as well, from maplins etc, the resistor formula is easy to work out if they are not 12volt ones.
tabetha