Lilac Night by Diamine is one of their 150th anniversary inks. I wouldn't call it Lilac. In my opinion it's a dark blue with hints of purple. In any case it's an ink you can use anywhere. Its appearance is professional enough for the workspace and the color beautiful enough for personal notes, correspondence and greeting cards.
The behavior is excellent. It feels and looks a bit dry on Clairefontaine paper, but surprisingly enough the drying times were a bit above average with just under 40 seconds. No feathering, beautiful shading, no show-through. Just what I expected from Diamine.
Water resistance is low at best, but you will have a chance to rewrite or accept. A few drops won't completely destroy your writings.
The color is a lot less purple than the bottle suggests. When compared to Iroshizuku's Shin-Kai however the purple hints are noticeable. However, when compared to Jurojin or Herbin's Amethyste, this color is very blue!
I have used this ink for a few days in various pens now and I really like it, definitely recommended!