Elmers (the glue people) make a line of paint pens; you can find them at WalMart. Lots of primary colors. I have red, yellow, and white... use them for labeling lots of items. For carto's you'll want to make sure you get a fine tip. Also, at craft places like Hobby Lobby, often have paint pens in dozens of shades and colors.
A quick easy way to draw a band on a carto: lay the pen down on a flat surface, and stand the carto up next to it touching the pen, and turn the carto. Place the pen on top of something, or the carto on top of something to raise or lower the band.
A quick easy way to draw a band on a carto: lay the pen down on a flat surface, and stand the carto up next to it touching the pen, and turn the carto. Place the pen on top of something, or the carto on top of something to raise or lower the band.