Hi, just trying to update a metal fronted light switch with a new plastic one but there seems to be wiring that I don't understand fully. There is a green which goes to the earth into the socket box in the wall (into a screw), yellow into the top of the switch block, and red and blue out of the bottom of the switch block. It only controls one pendant light. I'd be grateful if you could tell me what to do to change it into a modern plastic switch. I can post a picture of this helps. Thanks in advance