I have the first RHD roadster 660999 painted in twilight blue interior colour was noted in factory records just as Blue
The factory when they used the word blue in fact meant a light blue colour and when it was combined with a Dk Blue leather the interior colour was known as "Duo Blue"
The correct Connolly leather code for this blue is VM3244
A lot of serious and well known restorers get caught when they order Light blue leather they finish up with the connolly leather VM3230 or an equivalent of it.
Where the problem occurred in the early 1950's in that Connolly called VM3230 light blue and VM3244 grey but jaguar reversed the colour names.
So "Blue" sometimes referred to as "light Blue" is absolutely definitely the correct connolly colour swatch number VM3244 and when you get it it will be a gunmetal looking grey colour.
The best example of this colour on the net is at xkdata 660857 the trim as depicted is the original 1951 factory trim, it is correct see http://www.xkdata.com/gallery/zoom/?id=106515 and your leather should have this sort of grain in it.
Done properly this is a wonderful colour
Some trim suppliers 20 years ago referred to it as French Blue.
I would recommend you source a book titled "XK120 explored" by Viart
terry
tmcgrathatbigpond.com