Longarmers tend to use many different products to mark quilts. We also share the good, the bad and the ugly about various products that have had problems in the past...so that we never use them and ruin someone's quilt.
It's pretty well known to never use yellow or red anything, and this particular chalk is known to cause issues. (The heat from the needle is probably what cuased the yellow to set in.) In addition, if using chalk, it's best to use Miracle Chalk in either the washable or iron-away versions, white or blue. This chalk, along with the blue washout markers, seem to work consistently well without issues...unless they're heat set with sun/iron - then they won't come out.
We also share many tips to get out markings. It's been reported by a couple of people that Oxy-Clean has faded/bleached their fabric. Many have reported success with it, so just watch for the fading. Dawn is used well, and an alcohol mixture for pencil marks.
Hope this helps. Sorry it's too late to help you - and I sure hope it comes out! Maybe it will help someone else in time though. Keep working with it. Eventually you'll get it out, but it sure takes a lot of trial and error! At least the purple is out :)
Debbie in Austin