It’s all in where the lights are placed and how bright they are. Those were all done with one or two 600 EX RT Speedlites and some coloured gels. The bottom one had a single Speedlite placed below the bowl firing into the bottom of it, sort of using the bowl as the front of a softbox or shoot through umbrella. Shoot through bowl, instead!
The one above that had fairly high power, but the lights, one with red and one with blue gel, were facing toward the camera, 45° across the camera axis. No light hitting the white background, so it is black.
As the lights are turned more and aimed perpendicular to the camera axis, there is more spill onto the background, so it brightens and takes on the colour the gel provides. The colour gets deeper if flash power is reduced. The first one had the flash with blue gel aimed more toward the background and the red gel aimed across the splash. The second one used the same blue gel but the red gel was replaced with a yellow one. Angles and power were changed.
As an afterthought, I took a photo of the setup, after camera and flashes were removed. It is on Flickr. It just shows tripod head, bowl, background and water source. I have some of another setup, but I was using a different bowl and the flash did not have a gel because I was using a coloured background to colour the water.