This pen was the first M800 I bough way back in March 2011. The Blue o' Blue has since been over shadowed by the Vibrant Blue and Ocean Swirl but it was my favourite blue pen for years.
A lovely old M800 Fine nib that writes so well - I am probably harping by saying they don't make them like this these days.
This Waterman Blue-Black is the longest in use ink I own. I probably bought this bottle in the mid-2000s. It is the old formula that has a very distinctive smell to it. No real shading from this fine nib, but I can detect a tiny red sheen in a couple of places on the samples. This is the blue-black to which I compare all other blue-black inks.