First of all an apology... I tried to scan a comparison between this ink, Diamine Sapphire Blue and Waterman Florida Blue. Unfortunately, all three inks looked exactly the same!
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I rate Diamine Inks (so perhaps I am biased) but WES Imperial Blue is now my daily 'work' ink. Sapphire Blue is a nice colour but is quite vivid, Florida blue is probably the closest to WES Imperial - however, WES is more in the purple/redish scale of the spectrum.
Sapphire Blue was always a bit too bright for my work in the Pensions industry - think accountants who consider money in 70 years time BORING.
Florida blue for me was more greyish out of my Pelikan M215 which is what has finally convinced me of WES Imperial Blue. I would say that it is a nice, professional blue that is a 'toned' down version of Sapphire Blue. Higher contrast than Florida blue this is now MY ink.