Color is the most powerful element of art, and all works of art have it -- even so-called "black & white art (black and white are colors despite what many painters and art teachers may tell you).
In all periods of art one can find examples of line work that has been colored in from early printing to illustrated manuscripts to cave paintings. People seem to be hardwired to capture an object in lines and then add color.
Incorporating this element in a line drawing presents several interesting questions:
To Color or Not to Color?
That's a mute point since everything work of visual art has color. The question should actually be should one add colors beyond black and white. Black and white artwork is unique in that the viewer reads it much like one reads words. Black and white art tends to create an intimacy with the viewer and draw him in. That could easily be one reason why Japanese Manga is so popular and independent comics have such a following.
How Much Color?
Should a work be monochromatic (meaning one color with its associated shades, tones, and tints), or should it use every color in the rainbow? Should one limit oneself to two colors and make the most of them? The fewer colors one has, the more one is forced to design with them, and the more harmonious a work can be. The more colors one has, the less harmonious a work tends to be, because the eye and mind has so much more to process. But this extra processing creates a certain buzz and overload of senses people like, so there is a reason to go for it.
Flat or Gradiated?
Many early printed works were printed flat (meaning a block of solid color) because of technology. Just read old comics -- you'll find simple gradients but that's about it. When technology reaches a point that colors no longer have to be flat, a common trend is to go overboard and overrender a work to death. Just pick up a comic book from the 90s. Garrish. Even if one is using a monochromatic scheme, one can use a few greys, flat greys, or the full gambit of 256 greys.
So what's the Right Answer?
The right answer really depends on the question, and the question for coloring art is what is your ultimate goal or purpose. Once you know why you're creating a work, then the question of how to apply color becomes simple and obvious. Of course, answering the question of a work's purpose may not be so simple and obvious, but that's a question for another day.
The illustrations above were inked with a Japanese brush pen and colored in Photoshop. The illustration is part of the ongoing Wandering Koala serial that presents a page of text and an illustration each day. If you haven't checked it out, go there now and enjoy! The story is just getting started.