fitting a 2 way ceiling pull switch?

I have to install a new 2 way ceiling pull switch and stupidly did not check the wiring of the old one before removal. There is a bare wire, which I presume is earth which goes in the separate earth terminal in the mounting box. Then there is a yellow, blue and red wire to go in Com, L1 and L2 terminals of the switch. But what goes where? This is a bedroom light which is also operated by another switch outside the room.