I use Crayola Chalk to mark dark colored fabrics. But - it was a pain because there was never a sharp point. I was at Office Max the other day and they had these two hole pencil sharpeners and the light bulb went on. It was only 30 cents to - I went for it. When I brought it home I immediately tried sharpening a piece of chalk in the large hole of the sharpener and it works like a charm.
I know there are lots of chalk liners, etc. - but - this is just fine. And really cheap too.