I absolutely love the Pentel Arts Gel Roller for Fabric pen. It is so black and no fading yet. I used these again recently when making end of year gifts for our sweet teachers. My daughter wrote out the label first with the pen (she's 6) and then I traced over it a second time because she's never written with a pen on fabric before. Going over it a second time made it black black black and after I let it sit for a day, I heat set with the iron and then washed in the machine on hot, then warm, before gifting. There was no change in the label. It was still black black so I'm in love and will never use another pen. No more stamping to make labels, yay!
Link to the pens:
https://www.amazon.com/Pentel-Roller...1726395&sr=8-1
Added a picture so you can see the resulting label