In my Visual Development class I emphasize several aspects of rendering primarily dealing with the importance of grayscale relationships. This ultimately leads to how well a students deals with color. A good line drawing is great but once it goes to color the composition takes on a whole new vibrancy. This is an example of the lesson I gave on the subject back in 2002. On the left is the blue pencil / black line sketch of a character I came up with in class. On the right the completion of the demo with a rendition in color markers on a photocopy of the original drawing. Getting into color will significantly enhance your art. Especially if you're aiming to be a character designer or visual development / concept artist. The industry today is looking for more color work from students who are heading in the direction of production design. Having color markers handy or access to a digital illustration program such as Photoshop will help make the transition and take your art to the next level.