Painting tire grooves.. what paint?
 

I was just wondering if anyone knews what type of paint that comes in the tires pens you buy to paint tires. I have bought the pens before and they work awesome. But for $8 a pop I would just like to know what type of paint it is and pick some up from a hardware store. I have tried regular latex paint but it just peels off in no time. I know the paint in the pens are some type of latex paint.