Since many of the people in this community are novices at digital coloring, I thought I'd share the most fundamental "rules" and philosophies that I was taught, and that I learned for myself, about the art of coloring digitally.
Rule #1: No fuzzy brushes.This should be the first rule that every digital artist learns. Brand it on your mind. Your heart. There will come a time when you can break this rule, but when you are first learning to color digitally, put DOWN the fuzzy brush and walk/run away from it.
Instead of fuzzy-edged brushes, use hard edged brushes with low opacity and flow. If you are using a tablet and a program with pressure sensitivity, set opacity and flow to pressure. Then use patience and build up your colors slowly.
If you don't know how to do this, post and tell me what program you use, and I can help you find the settings and maybe post some screen shots.
If you want to take this a step further you can get yourself some nice custom brushes that simulate what you were probably trying to achieve with fuzzy brushes (gradual color changes). But those require knowing the software a little more. For the time being, a basic hard-edged round brush with low opacity is your best friend.
Rule #2: Dodge/Burn are The EvilOK, so this may have changed a little in Photoshop CS4, because they gave you the option to have dodge/burn not change the hue, but even as it is it still has problems. And as with rule #1, there will eventually be times when you can break this rule. I know some people who break it with impunity and create goooorgeous art, but they are the exception, not the norm.
Dodge and burn are not good tools for shading and lightening your art. They produce odd colors and things look fake.
If you want a simple way to create darks and lights, take advantage of layers. Create a layer set to "multiply" and draw your shadows on that layer (using the same as your base color). Create a layer set to "screen" and draw your highlights on that. It won't help you produce photorealistic shading, but it can look attractive and save you time.
Rule #3: The internet can teach you how to drawThe internet is
full, and I say
FULL, of digital art tutorials. Deviant Art is especially full. I mean, seriously, you have no idea. It's glorious. And that site is only the beginning.
If you want to do something and you are not sure how, go to deviantart.com and search on it. "coloring skin tutorial", "fire tutorial", "chainmail tutorial", etc etc. There are soooo many generous, talented people out there giving advice on how to use digital art programs.