I could spend a lot of time, waffling, to basically tell you that I don't know, but suspect that the Purchasing Commission would have just specified "green," and left it to Consolidated.
When the Spitfire prototype was ordered, the spec was simply "grey-green," and, judging by a 1941 Mk.I, Supermarine used the same green as they'd used on the S6B.
The Air Ministry were very specific about exterior colours, but I've never seen any evidence that they were similarly pedantic about interior shades.