According to Allure magazine's February 2013 issue, Cobalt is the color of the season. The inky blue is sophisticated and intoxicating and works best with shorter nails.
Recommended shades are OPI's OPI...Eurso Euro, which puts a darker edge on midnight blue, and Jinsoon's Blue Iris, which is a good bridge between the cool grays of winter and the brights of spring.
Shades this intense look best with a high-gloss top-coat. Tell clients to reapply a formula such as Essie Let It Shine Top Coat every couple of days to maintain the shine.