CharlotteK
Yes, I used a Sharpie and I had to go over the cards many times to reduce the shade difference with the grey. It looks good though. It would definitely suit Tinker's Damn, this is the closest deck I have to the TD deck style wise.Dark grey looks great for this deck!
For my Tinker's Damn I think it would be a great choice as well; I read in another thread that Avery Marks-A-Lot are impeccable and I don't want to take a risk (if the marker leaves a few traces for example on my hands or on a cloth bag, I don't know).
Nevertheless with Avery I didn't find a lot of colors, therefore I ordered some black markers.
Sharpie markers (I guess you use Sharpie) offers probably more choice!
In any case, Dark grey looks a good choice, probably better than black!