The physics of light is very complicated (is light a particle or a wave?). And we're not talking about a mirrored surface. The physics of light passing through a boundary line like water/air and water/glass/air adds another level of complexity along with the "angle of incedence". Very simply put, Light passing from air threw the air/water boundary then hitting the water/glass boundery is reflected back into the water then strikes a surface (like a fish or rock or chromoprotein of a coral, flourescent proteins add another layer of complexity as they are absorbing then emitting light) and some wavelengths are absorbed and some are reflected giving a fish or rock the color of light that is reflected (here's where the philospher's mind bending question comes in "can we trully see something?").
