Step 3 : Base Colors
I treat coloring in multiple stages, the first of which are the base colors. Base colors are important because they help establish the over all color tone of an image before you get too deep into an image to make adjustments. They help give you a pretty good sense of what the final image might look like.
I begin first by adjusting the colors used in the line work. This helps me visually separate the areas of the illustration that are drawn similarly yet have different tones. This also helps me get a high level sense of the colors I want to use as fills.
Next, I add the fill colors. It's important to find colors that describe the material of the object in the image, but you also have to ensure that the color feels like it belongs alongside the other colors of the illustration. I'm no expert on color theory, but I feel the colors I've put together work nicely.
Now that I'm happy with the base colors, I can move on to adding more detail, shadows, and highlights to my colors.