I have now used the colored Sharpie "ultra fine" point pens, as I purchased a set of ten at Target. I had used the "extra fine" point before, which many designers do - and which only comes in the red, blue, green, and black. These are perfectly safe - and so are the new ones in more colors! I chatted with Sanford several months ago about the inks in their various pens, but these were not available at that time. I drew on canvas with each of the colors, and have poured water on the canvas, "spilled" Sprite on it, spit on it and rubbed hard - and I am unable to budge or smear the ink in any way, just a few minutes after the drawing.
These are also available on the internet on the Sanford site in a set of 12 - the extra two are yellow and brown, which I can do without. These will be great for drawing on canvas, as sometimes even the paint in a light color won't cover the black lines made by a black pen - which is all we have had for many years.