Clover White Marking Pen (fine)
The ideal marker for sashiko or marking other dark cotton fabrics, the Clover White Marking Pen is like a rollerball, and produces a fine line, which goes white as it dries - you need to allow a few seconds for the line to show. The second photo shows the line just after drawing, while the third shows how it dries white. The fourth photo shows the Clover pen line at the top and the Sewline Fabric Pencil at the bottom, for comparison.
No need to press hard or scribble the line back and forth, just normal drawing pressure is all you need. This marker is particularly good on very soft fabrics, like Azumino cotton. The marks don't rub off easily like chalk lines can do and will stay on well even in warm, humid weather. The lines wash out and can also be removed with heat (such as by pressing).