There are lots of "disappearing ink" pens but this is our favorite. Your markings can be quickly removed with water. It's especially useful for marking light-colored fabrics where chalk doesn't show.
Clover Water Soluble Pencil-White, Pink & Blue : Quilting Supplies : Arts, Crafts & Sewing
Sincerely Quilt Pattern (Download) — Eudaimonia Studio
Strawflower Quilt Cover Kit by Side Lake Stitch – Pasadena Quilt Studio
Water-Soluble Marker - Fine-Blue
Clover Water Soluble Pencil-White, Pink & Blue : Quilting Supplies : Arts, Crafts & Sewing
Water Erasable Marker (Thick) – Clover Needlecraft, Inc.
Water-Soluble Marker - Fine-Blue
Water Erasable Marker (Fine) – Clover Needlecraft, Inc.
Clover White Marking Fine Pen (517)
Black Fabric Markers 2 Pack, Broad and Fine Tip, Water Resistant Ink, No Steam or Iron Needed
Sonoma Trails Quilt Pattern PC-247
Clover Water Soluble Pencil-White, Pink & Blue : Quilting Supplies : Arts, Crafts & Sewing