Last month I was teaching in Fort Collins, Colorado at AlwaysBCreating. On the way there, I stopped at Two Hands Paperie in Boulder. I haven't been doing that much shopping because of everything going on this year.
I was very happy to find a new toy, "Chalkboard" or "Midtown" White Chalk Pencils made by The Pencil Factory in Nashville, TN. Please note that the link above they are SOLD OUT but, if you look to the links below or do a google search, there are others that are selling them.
As you can see below (on dried, black acrylic paint as well as the journaling, "she hides her secrets), the white is a vibrant white on dark acrylic paint. I've rubbed it with my finger and it doesn't go anywhere. I have not erased it but I will try that soon (it will lift the paint to some degree so I will do it on a test page. Apologies.) You can paint over it if you don't like it. For $14 for eight pencils, it was a good deal and I LOVE the vibrancy of the white.
I've read different reviews that said it doesn't work on actual chalkboards, so there's your warning.