During a recent lecture on the use of confocal microscopes, we were told that red light penetrates further into tissue than blue and green light.   This was demonstrated by the fact that a red laser is still visible when shone through a finger, but a green one isn’t.   This contradicts the loss of red light that is observed as you descend underwater; everything appears blue at depth when scuba diving.   Why is this?

Description of image: It has a tiny hole in it (almost visible in the pic) and hairline fractures (not visible in pic). Image taken using a USB microscope. Found the object on my shirt cuff. it measures 0.9mm diameter and is spherical.