Whilst most colored pencils are wax based, some brands use an oil based lead, like Faber Castell's Polychromos. These pencils are very soft to apply color so will cover every fibre of the paper with their bright hues, but they are also very expensive and should only be considered if you are looking to take your art to the highest level.
Color Outside the Lines Sometimes. In some circumstances, like this one, you can color outside the lines because you'll cut the piece out afterwards. This allows you to use large consistent strokes, as you can see in the red kidney above and on the right. This is an especially helpful tip for younger students who are coloring the organs in this My Body project. (Just be sure not to use this tactic on the upper half of the heart in the My Body book because we won't trim around all those veins and arteries.)