Can't say for sure off the top of my head (and I'm stuck at work for another 8 days so I can't check) but green/white rings a bell. 3rd one along on the connector IIRC. I have a set of very sharp probes on my meter, so I can pierce cables to measure what's inside them. I found the right one this wayI have one to fit soon, can you recall what colour the wire was on the beeper box?
(If I'm honest, I found the wrong one first, since I wasn't paying attention!)
Like the idea of a roof view camera for barriers!