The colour appears to be Royal Blue.
Originally the car was painted what appears to be Carmine Red.
Royal Blue is:
Triumph code 56
ICI code 4665
PPG code 13126
Production years 69/70/71
It could also be Sapphire Blue, but this was a later colour 72/73/74, so would not be period-correct.
The Triumph paint codes and dates of use are here:
http://www.trregistry.com/start/registry/html/painttrimcodes.php
They are also here:
http://www.geocities.com/motorcity/speedway/1080/paintcodes.html
And here. This site has some photos of cars sporting the various colours. Very useful!
http://www.teglerizer.com/triumphcolors/index.html
E.g. from the teglerizer page
"Dark Blue"
(They give paint code PPG 14871 for this, which is the code for Delft Blue. Delft Blue is not this dark, and in fact they have a Delft Blue car pictured further down their page. I think the car pictured above is in fact "Royal Blue", and the same paint as the GT6 below.)
"Royal Blue"
"Sapphire Blue" 
My car
Which is it?!!!
Back to Overview