many quilters use pencil- chalk tends to brush off before the quilting is finished.
i've been using pencils for years- i've never had one not come out-
when the quilt is laundered the pencil will wash away-
there are a number of different marking tools on the market- some are----blue water erase markers, air erase markers, frixon markers (which disappear when ironed) chalk and a bunch of different pencils...those are just a few available-
when quilting on white always test to make sure your choice will in fact wash out after the quilt is completed-