All three are continuous random sounds, generated mathematically in your browser. No file is downloaded; the sound never repeats.
Brown
A deep, smooth low-frequency sound — like rain on a window or a distant waterfall. The bass dominates. Most people find it the most calming for long sessions; least fatiguing.
Pink
Steadier and slightly brighter than brown. Like steady rainfall or wind through trees. Often used by audio engineers for room calibration. A middle ground.
White
All frequencies at equal power. Crisp, hissy, like an untuned analog TV. Strongest masking of sudden environmental sounds, but more fatiguing over long sessions.
Try one for a few minutes. If a color doesn't suit you, switch or turn it off — Ómbre's job is to disappear, not to convince you.