Yes. I believe the basis of the darkness of water as it deepens is purely a case of energy conversion. Conservation of energy states that energy cannot be destroyed, only changed to different kinds of energy. As light strikes water, the energy begins to be absorbed, and most (if not all) becomes heat. The less light is reflected, the more it is absorbed. For example, dark clothing and asphalt heating up more on a sunny day, while lightly colored clothing and surfaces reflect more light, keeping cooler. As for gravity effecting light, it is, as Christian95 stated, more of a side effect of space-time being, in effect, altered/warped/bent as mass increases. This is why light can’t escape a black hole, as it really has nowhere to go. The one caveat there is Kruskal–Szekeres theories involving white holes. Where black holes can be entered but not exited, white holes cannot be entered, only exited. This, however, is theoretical model that is not applicable to black holes caused by gravitational collapse, but rather within theoretical models of eternal black holes (in Kruskal–Szekeres coordinate systems. It gets even more confusing and in depth as the man Hawking suggests that a black hole and a white hole are actually the same thing, where (and forgive me if this is the wrong interpretation) a white hole expels matter in the past, and a black hole pulls it in in the future. I think there may be one or two decent documentaries on this subject if you look through some of PBS.org’s streaming video selections. Hawking discusses black holes a bit in one of his “Into the Universe” documentaries, namely the one on time (as one of maybe two certain ways to “time-travel” to the future), where a capable vessel could orbit a black hole, in effect slowing it’s own time, so when it left orbit, the outside universe will have aged much faster.