yngldy

Been there! You can use cheap aerosol (not pump) hair spray to keep the chalk on the quilt. Just don't spray too close as you will blow the chalk off. Haven't tried it on blue chalk. Maybe test first? Heard blue is tricky to wash out. Golden threads paper or tissue paper works OK, but if you have a lot of crossovers it is hard to get the paper out from under the stitches.
I use Crayola washable markers when I mark, and don't remember not showing on dark fabric. If you can't see it, try another color. If I remember correctly, orange is good on navy. It can't be seen from across the room, but it will be a couple shades darker than the original.
A couple weeks ago, someone on this board said they use Pellon 541 washaway. I bought it, but haven't used it yet. I did mark on it, worked good. Cut a little piece off and it dissolved right away. Got it at Hobby Lobby, used 40% off. Someone said Joann's has it too. It is on a bolt, not in a package. I was thinking I could use glue sticks to glue the scraps together for smaller projects or spaces, so that nothing goes to waste. You might want to check it out. There are two kinds of washout. One looks like plastic. You DON'T want that one. The correct one to use looks kind of like the fabric they use for the cheap "fabric" grocery bags they sell at markets.

There is also something called a Haro marker. It is a semi sharp edged plastic tool that "presses or creases" a mark on the fabric. Haven't tried it, but have seen it used on TV. I have seen it at Joann's in the notions. Good luck!