It was the colour used by BRP - Stirling Moss’ father was one of the partners and Stirling drove for them when not under contract.
The team name changed to UDT Laystall racing after one of the very first sponsorship deals….there are quite a few different types of car that you can find in period pics painted in the same colour, Lotus 18, 19, 24 and Coopers, BRM’s etc.