Thank you so much for all of the suggestions. Now I'm completely confused!
The suggested ink which I like the look of most is Diamine Violet, though there seems to be some disagreement as to whether this is water-resistant. This is also an ink which I can easily source.
Some of the suggestions are too blueish for my taste; I would like a more pinky violet.
Pelikan violet also looks nice, but I seem to remember reading someone mention that it isn't water-resistant.
Scabiosa is one of the too blue and heavy (on my monitor) inks, and I don't think I dare touch an iron gall or a heavily pigmented ink like Noodler's.
I'm not saying there's anything wrong with these ink for someone more scrupulous about caring for their pens.
The Jane Austen ink is a nice colour, but there was no indication of its water-resistance.
Has anyone done water-resistance tests for the Diamine Violet?