My favorite fountain pen ink brand is - without hesitation - Iroshizuku. Excellent behavior, a beautiful bottle and some amazing colors. Tsuki-yo (moonlit night) is the first Iroshizuku ink I ever bought, roughly seven years ago. A beautiful dark teal color. It's a dark blue but with a very clear hint of green in my opinion. Which makes it perfect for any situation, both personal and professional.
This ink deserves and demands high quality paper. If for some reason you cannot use that, please forget this ink brand. Buy Noodler's then. But if you can and do use it, you will be rewarded accordingly. The ink writes like a dream, very smooth! No feathering, no serious show-through, wet but with acceptable drying times, and very beautiful shading. Water will damage your writing, but won't wash it away completely.
At first glance this is a decent, serious dark blue. After that first glance, the uniqueness of the color will shine through. I highly recommend this ink, this is not my first bottle of the color and I still fill one of my pens with it on a regular basis.
N.B. Written on Original Crown Mill Vellum paper (white)