Here is my review of the OS Teddy Roosevelt Midnights' Blue. This ink was a special edition for a pen show I think, and Anderson pens had some extra OS, so I picked up a bottle. I don't think it's available at all any longer. The label color bar looked like a deep dark blue, and I love those kinds of colors. The ink is quite far from deep, dark blue, and much closer to OS Mark Twain Halley's Comet. This ink is a bit more muted in tone than the Mark Twain.
On Moleskine, I originally didn't like it as the color came out too pale, but it's certainly usable and not bad looking. On the better paper (Mohawk via Linen) it looks nice, is quite shady. But it's not that much different from OS Mark Twain.
I'll get up on this small soapbox right here: I really wish ink producers and retailers would stop calling violet and purple, "Blue". Those two colors are not blue. They have their own names. And they are not the same thing. It doesn't seem that hard to look at the color of something written, and use the color picking software on the computer to find the right color for printing on the label. No one expects it to be exact, but if the ink is violet in the bottle, and when you write with it the color is violet, there's no reason to put some other color as the indication of what the ink looks like.
Many people are buying ink over the internet, they never get to see the actual ink nor write with it. They rely on the descriptions by the retailers, and the picture on the box (if any) of what the ink looks like, what color it is.
OK, I'm done now.
I like the color, it's just not blue, and it just seems very similar to OS Mark Twain.
The first two pictures are scans from the crappy scanner.
Now here are pictures from the iPhone. These definitely show the color as darker than it really is. The scans are closer in that regard.