I took a class on FMQ recently and there was quite a discussion about this and a lot of the gals had already had experience with the white and colored chalks.
First off, the new white chalk is an iron off chalk. It will iron off with a dry or steam iron. I played with it and it did disappear, sometimes slowly, sometimes quickly, but it always disappeared.
Now, be sure you get the new chalk. They are still selling the old chalk, it does not say iron off on the package.
Several of the ladies had tried the colored chalk and they all complained that it did not come off easily like the white chalk did. It's cranky and no one recommended it. The general opinion was that something in the coloring process gave it an "iffy" property.