Those "liquid" lights like that actually have more in common with the old plasma globes than with regular fluorescent or cold cathode lights. The tubes are usually filled with an argon/xenon mixture and are driven with a high-frequency high-voltage power supply. The result is a plasma streamer that goes from one end of the tube to the other, usually along the tubes surface. The streamer itself will be white, but they can be colored by coating the tube with a phosphor.
The effect over water would probably be pretty interesting.