First, I use a 50/50 mix of Diamine Midnight and Diamine Eclipse. The Midnight is just too light colored for me after it's dried, and the Eclipse is too dark and close to purple on its own, but together they make a very nice blue-black.
My wife and I were vacationing in Jacksonville Beach a few weeks ago and my Kaweco Classic Sport came unscrewed in my pocket while we were walking on the beach. I didn't realize it for a while, so I had a large, blue-black stain (quarter sized) in the pocket and a slightly smaller stain (nickel sized) on the outside when I finally found out. I was mad because they were the only pair I had with me and the pants were still new. I knew I had at least 24 hours before I would be home to use the washing machine. Until then, I just wore them--this time, leaving the Kaweco in the hotel room. We drove home the following day and made it in just before midnight. I was tired and collapsed in bed, forgetting about the stain until the following morning (T+36 hours). I rain the washer on warm, pre-treated with Shout, and used Tide Cold Water. 30 minutes later when the cycle finished, there was no trace of a stain.
So... maybe the original question was about a different kind of staining, but you should know it's possible to wash out Diamine just in case something goes awry.
Enjoy your new inks!