Start at the inner top corner and paint a diagonal line to where the free edge of the nail begins with a cobalt blue polish. Beaudreault recommended using Essie Nail Polish in Butler Please ($9), and we also love Nails Inc. Nail Polish in Baker Street ($10). "A good place to start is on the outside of the nail's moon," recommended Beaudreault. Fill the shape in with the blue paint, then apply a second coat till it's opaque.
Courtesy of Paintbox