according to Leslie Jackson (who shows a tricorn in what appears to be this colour), this is dark royal blue (cased blue) - a colour replaced around 1969 by kingfisher - and although these vases appear not uncommonly at times, don't recall seeing this colour before.
But more of interest is the unpolished base - which made me wonder if the Chinese were now producing tricorns - and the obvious fault on the rim, which suggests this is a second, and a rather wonky one at that...........I'm surprised it managed to leave the factory.
Anyone else seen such a reject looking example of a tricorn??