#2 pencil. I was going to mention that, and forgot to! Haven't tried a grease pencil. All of the paint pens that I've tried have faded faster than anything else I've used. I'm going to try nail polish next. I think if you had dark markers, White Out would even work great. I've used White Out to cover a chip in an old bathtub before, and it never seemed to wear off, even though it got wet every day.
