1) There is no such thing as "The correct colour" for any BSA that did not have a full baked enamel finish, and even then there were variances.
BSA bought in paint from several suppliers in batches and no two were identical.
2) No matter what colour you paint your bike, 60% of all who look at it will proclaim "that colour is wrong"
3) Very few bikes left the factory with consistant colour from one end to the other.
4) Parts were made ( and painted ) in batches of the same item, not in "bike lots" so different people would have painted each & every part. Some were sprayed, some were dipped and some were brushed.
5) The pinlining was a hand brush finish so no two will be identical in colour, size & shape.
6) Diferent parts were made at different factories and only came together on the production line.
7) some parts will have different base coats and any part that was diverted from the spares division to the line will generally have a black base coat and this will show through the top coat. It made the golden flashes slightly green ( my favourite finish ) and the maroons really deep tending purple red.
The only original A 10 owner I know has a favourite story when he bought his in 1950 from the first 20 to be sold in NSW.
From the first batch of 20 bikes , only 2 bikes were the same colour from front to back so he made the dealer take his showroom extras off the bike they had fitted them to and put them on the bike he told them he wanted to buy.
The other "single colour" bike went into the window display.
When he came in for his services he noted that the second bach ( about 40 ) were even worse colour wise so he was happy that he had paid the extra premium for a pre season order.
So don't beat yourself up about finding an exact shade. There isn't one.
Find some thing that you enjoy looking at and go for it.
If jibes worry you then just remember "Grea aunty Alice" who worked at BSA and liberated the "original tank on your bike " to replace the one damaged on your father's bike which he did not fit beacuse he thought it would add value when he resold it and you got it from your fathers estate still in its original wrappings.
The enjoy all the crap they come up with to justify their criticism .
Ken used to keep his original sales receipt in his wallet .
He would listen carefully to the "expert morons" going on about how wrong his bike was, follow up with "well it was like that when I bought it" then produce the 1950 receipt and leave the clots where they belong, flattened on the ground with a big hole in their creditability.