Try a few, or all, of these exercises, and you'll be "seeing red" -- in a good way, I hope.
For the first 5 RED exercises, you'll need your sketchbook, a pencil, a black pen, some watercolor pencils or colored pencils, some w/c paints, some magazines (you know you have some old ones lying around), a glue stick or "Yes" paste, and scissors.
1) Draw a part of a red motorcycle, bicycle, tricycle, or wagon -- Draw a contour line drawing, with a black pen. Don't worry about proportions, or whether you've drawn it correctly. This is your sketchbook -- it doesn't have to be perfect. "Perfect" is boring, anyway, don't you think? Then, add some color, with a little red watercolor. Add some shadows with cross-hatching in pen and a simple gray wash (or touch the edge of the black pen line with water to make a gray wash) . . .