I use Rohrer & Klingner sketchINK in Twsbi Go pens
I have four pens with different nibs with different ink colors
The inks are excellent for watercoloring, dry well and fast, and have a strong enough color to show thru if the watercolor is transparent
The are also strong enough to ink after painting
I leave the inks in the pens for weeks on end and have no problem with drying out, and the pens start up immediately
I recomend the inks and their range of colors