Years ago at Malvern Quilt Show I asked a well known UK hand quilter - Sandi Lush - what she used because I could see coloured pencils beside her. They were watercolour ones - the type you use to colour in a drawing and then go over with a wet paintbrush to achieve a watercolour painting. Found some in my local stationers and they are very good. Lots of dark colours for the light fabrics and vice versa. I always wash my quilts when finished cos they're always grubby by the time they're finished and the lines just disappear even those where I've been heavy handed. They are soft and need sharpening often. I've been happily using these ever since and have never tried the air disappearing or the water soluble markers.