It’s time for another Terrific Tool! Have you tried Frixion pens? They come in a rainbow of colors, widths and even highlighters. Basically, heat erases the markings and cold brings them back (which is important to remember if you’re shipping a quilt as it will likely get chilly). When you wash the quilt, the Frixion markings are gone completely. I always test the markings on each fabric because there can be a “halo” left on some fabrics. I’ve found lighter fabrics work best with these pens.
I found this great one on Amazon that offers four color options!