Hi Tom,
I see you have TR3A. I think the same BRG was used on those as on TR4 up to January 1963 (see below).
Later TR4 (from CT19519), TR4A, TR250/5 and TR6 were offered in Triumph Racing Green (Martin Senour Paint code 25426, Triumph code #25). This color is rather bluish and is sometimes refered to as "Connifer Green". In fact, the background of the page Tim liked to in his post is similar to this color. I have seen it mistakenly called British Racing Green by some paint manufacturers.
A British Racing Green was again offered later in production, on TR6 beginning in 1975, but I don't know if this matches the earlier BRG.
Earlier TR4s were offered in a British Racing Green (Martin Senour Paint code 25099). I don't have a modern paint code for TR3A, but do have the original brand codes (from Bill Piggott's "Original Triumph TR". Perhaps you can cross reference these somehow:
Dockers BF5092, BF5761, BF5531, CGG40 or CHG65
ICI Hilux M-048-2855
Pinchin-Johnson PJ 428HS, PJ 428LB
The Martin Senour colors referenced above can sort of be seen at
https://www.vtr.org/maintain/paint-charts/martin-senour-colors.jpg But, I must warn you this chart looks rather old and discolored to me (or perhaps a poor scan).
Okay, it isn't a Triumph, but to my eye this color looks pretty close to the TR3A/early TR4 British Racing Green:
Here's a Spitfire that's painted in a color more like Triumph Racing Green (although it's a PPG Paint code FM76954 or PPG 45102, British Racing Green):
Hope this helps!
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