I obtained the HMS Tamar colours via a Freedom of Information request to the MOD. There were five names listed. Four of these are standard BS381C colours. The fifth I'm not sure is really there (but it may be) but so far I haven't been able to track down what it is. It may take a visit to the ship with Nix Pro Color Sensor in pocket to zap some digital colour measurements.
It seems the HMS Severn team spent some time in the library at Portsmouth reading stuff, and I believe there are copies of some of our papers in the box files there now. We were never contacted by the crew prior to me starting a company Twitter account on Sunday, so I was quite surprised to see us mentioned there. I wish they'd got in touch sooner as I fear their conclusions may have been unnecessarily tainted by the physical samples they definitely viewed at Portsmouth. I've both seen and digitally measured those samples and unfortunately they are by a large margin the worst samples I know of in existence in terms of their age-related deterioration and colour shift.
E.g. the Admiralty Pattern 507C sample card they had has turned to a creamy-coffee colour
Those badly yellowed 80 year old linseed oil paint samples could unfortunately lead one to the false conclusion that the paint colours were all over the place in service, and it seems from reading Twitter that that is what they concluded.