One of the hottest hair colors of the moment is "ombre," a French word that literally means shaded like a gradient. You'll notice here on formerly blonde Kristen Wiig that her roots are darker while the hair is lighter mid-shaft -- as though the sun naturally lightened the hair in the summer and then fall came around and the hair grew out and...well you get it.
This is literally the hottest hair color of the season. Check out this article on "ombre" hairstyles in Allure Magazine.
Also check out this photo gallery of "ombre" hairstyles.
The 15 Hottest Hairstyles of Summer 2011.