I use a water washable graphite pencil which can be found in art stores. They come in different hardnesses and are black (the ones I prefer). They wash out in a regular laundry load.
I mark heavy enough so I can see the line well and it doesn't rub off as I move my hands over the quilt. Years ago I sold these at the register in my shop along with a very sharp little one inch square metal pencil sharpener. I had a piece of light fabric and a piece of dark fabric on the counter where anyone could try them out. The pencils worked on both. On the dark fabric they leave a shine that is easily followed, especially if the light shines from the side of your work rather than the top. Sold a ton of these things.
Unfortunately the Berol Aquarelle Prismacolor brand I adored is no longer made - discovered this after an exhaustive search through England last summer - but there are other brands sold in the states. Just google "aquarelle pencils." You'd probably prefer a medium rather than soft lead.
Jan in VA