Yep, stay away from Area lights, as they take forever to render. You can adjust directional lights (like your duplicated sun) by editing it's color. Edit the value of the color to adjust light intensity. Edit the hue to affect overall light color.

It's an old architectural rendering trick to put blue (cool light) in the shadows. It offsets nicely the warm glow of the sun, and typically is a function of the reflected light from the sky. You are certainly welcome to use any color you like.

It's not unlike painters using green as an underlay color for building flesh tones on a portrait. Complimentary colors, even subtle ones, add a pleasing effect to a picture.