You can pick a turtleneck in a snappy color and just pair it with dress trousers for a casual look or go tone-on-tone with a suit and a turtleneck as they did at Calvin Klein and Salvatore Ferragamo for a more sophisticated style.
In the Colors dialog box, click the Custom tab, then click in the Colors display to choose a basic color, and use the shading slider to the right to pick the exact shade you want.