Yes, I’ve actually been studying that. The deep‑sea anglerfish, for example, has a skin layer full of melanin that absorbs almost all the weak downwelling light, and underneath that a thin retroreflective layer that scatters whatever little light is left so it matches the random speckle pattern of the bioluminescent background. In my last dive I logged a specimen about 12 mm across, and the contrast ratio on the spectrogram dropped to almost zero when the ambient light fell below 0.02 lux. That makes it effectively invisible to predators that depend on contrast. I can pull up the raw data plots if you want to dig deeper.