Hair coloring creates dimension in your hair. It also amplifies and give your overall hair more volume. Take a look at the example above from hairstylist Hollie Jacques of Lux Salon. The client already have layers but the solid black color (on the left) makes the hair look dull and boring. Hollie brought it back to life with balayage technique up the hair shaft and a few trims to mend the damaged ends.
Here is another example of subtle coloring and "wow" after effect. Hairstylist Erin Dourmet used balayage technique to create a caramel swirl finish on her sister's virgin hair. To get a similar effect the highlight should only be a few tone brighter than your natural hair color. Also, try to visualize the natural flow and pattern of the hair to get this result.
If you're looking to give your hair a fresh new style and can't commit to a dramatic change, try balayage!