Exterior pond lights should be subdued white lights used to make the surface of the water glow, or to accentuate a waterfall, prized plant or other feature. These lights are installed at ground level along the shoreline of the pond.
Underwater lighting is commonly used to highlight fountains or sculptures. Use underwater lights sparingly, it is easy to go overboard. If you want to see the reflection of the moon in your pond, don't use underwater lighting.