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.)
If you have a corner or turn that makes it really awkward not to change direction, you can either color using curved lines or color using very small circles instead of lines. Just keep in mind that how you color will always be visible and will create the appearance of texture.