Diatomaceous earth dropped in swirling water, lit by an RGB pixel set to cycle through all full brightness, full saturation colors in the same period as the camera’s shutter speed (every half-second for this image).

Below are some other images I got with this setup which I liked just as much, and which I think capture the intended effect of the LEDs much better! The main things that vary between them are the shutter speeds, materials dropped in the water (some use sugar or salt), and whether or not the water was rotating.