A key has been added, written on Clairefontaine paper, with a number of different inks for reference.
Standard Disclaimer: Image provided only to give a general sense of the color. The vibrance and nuance are typically lost when an ink is digitized.

Review
When I write a review, I first focus on color, and award an ink 0 to 100 based upon that alone, separate from other considerations. I then deduct points from the color score for defects (ie: lack of flow, creep, etc), to arrive at an overall score.
Color
PR Midnight Blues is a nice, perhaps prototypical blue-black. In my pen, it comes off as “powdery” and dull, but I imagine a broader gauge would improve things.
Color Score = 85
Deductions
Midnight Blues didn’t perform horribly on the water test, but it left quite a bit to be desired.
-2
Overall Score = 83