Okay - I googled "chalk quilt marker that won't disappear" - or something like that and got a suggestion of vinegar. Nope.
So far - rinsed in washer, soaked in OxyClean, rubbed gently with vinegar, sprayed with Clorox's version of Spray and Wash - for colors, washed gently in machine with Arm & Hammer's detergent with OxyClean. The quilt lines where I did NOT sew - changed my mind - are gone, but the ones where I did sew the thread is now blue. Faintly blue, but blue - on my pink fabric. Guess it's going to stay that way. It's a table runner, not a quilt - so not quite so much time/money invested, but ... I certainly won't be using blue chalk again - unless it's on blue fabric - and then I won't be able to see it so ... what's the point?
It's a bit more obvious in person than in this photo - but it will be okay. The runner is still wet from the washer so it's more wrinkly than it will be.