Hello Ian and welcome aboard our friendly forum.
Going by the BSA Twin Restoration Book the 1951 A10 GF was available in either black or BSA Devon Red but depending when, in 1951, yours was produced, there could be a problem that I will cover later.
Basically, throughout the BSA production, particular models were painted in particular colours for particular years.....but you could always have a Black one as an alternative. So you can make your choice. Unfortunately the blue/turquoise colour you mention will not be the original colour for your model.
Painted items are as follows...frame, forks, oil tank, battery carrier, chainguard and mudguards. Most fuel tanks were chrome plated in 1951 and had painted panels to suit the rest of the bike. These panels were lined in gold whether they were painted black or red. The wheel rims were also chrome plated and had the centres painted to suit the rest of the bike. These rim centres were also lined in gold.
Other chrome plated items were the headlight rim, handlebars, fuel tank filler cap, brake backplates, battery strap, fork oil seal holder and exhaust system.
Right, here is the problem I mentioned earlier. In late 1951 and running through to 1952 there was a nickel shortage so chrome plating had to be restricted. This obviously affected the BSA company and it was decided to have the fuel tanks painted in matt silver and the panels painted as described above. The brake back plates were also painted over this period. The remaining chrome plated items remained unchanged.
So Ian, depending on how authentic you want your bike doing, you need to choose a paint finish of either Black or BSA Devon Red, then find out exactly when the machine was produced in order to see if it was affected by the nickel shortage.
Good luck with the project and keep us updated with the progress.
Beezageezauk.
