Try Multi=Pastel Chalk pencils in either white or light grey. they erase and are washable. I believe any chalk should be brushed off before washing as chalk will cake.
the Multi Pastel is a combination of chalk and clay.
Some like the Sketch and Wash which is a washable graphite. Looks deadly but also erases and washes out.
these three are made by General Pencil Co and available in some quilt shops and in an art supply store.
I would recommend avoiding a chalk with color as the color does not often come out when washed.
The new cermanic mechanical pencil is working for me on black batik. Brands are Fons and Porter, Sew Line and Collins and available in the big box fabric store.