A good Tattoo Artist should be able to mix an blend colors and also do shadowing work easily. It is fun to show colorful artwork like most of the tattoos we've seen as well as some black with shadowing. Here's some pics of Great Tattoos.
As you can see, Japanese Tattoo has become popular (exept back in the days in Japan) and a few of the reason is the ability to decorate the body with colorful designs by a well skilled artist. Some people prefer to have a Japanese tattoo done the traditional way while other opt for machines or both.
Regardless of the style you choose what you have to keep in mind is to give proper care to the new Ink so it won't fade or get infected, most important is to see a reputable artist, ask him questions and be open about what you really want on your body.