Not sure on the RAL. Thought it might be 7001 but thats standard silver grey and may not have the amount of flake in it required.
Did a bit of digging as I’d also love to know, but cant find a definitive answer as most seem happy to quote BMW Deutsche/German Silver and get the result they need.
As Rockhopper says, 144 is standard BMW silver too and will be a good if they can match against that ref number.