In fact, there are 3 primary colors. < There aren't only 3 primary colors if we're gonna be accurate. Primary colors constitute a set that can be combined to make other useful colors, but the primary colors you use don't have to be restricted to red, green, and blue.

Water acts as a selective filter. If a white light is suspended above a tank of water that was 1000' deep the colors from the white light would be filtered out selectively (one-by-one) as one descends. It is gradual. There is no abrupt interface. For example, most of the red is gone from the light after 10 feet. Some of the orange is gone. Less of the yellow is lost, etc. At 25' most of the orange is gone. At 35' most of the yellow is gone. This continues through the spectrum until all that is left is violet light and that fades out after hundreds of feet. So, at the bottom of this 1000' tank of water there would be little or no light! < Gonna add to this. Impurities in water has a lot to do with light absorption and scattering as well. These can have a huge impact on how different bodies of water appear with regards to their color. The colors that actually penetrate water is also impacted by other factors, such as the amount of light scattering done on rays of light by the atmosphere and the angle at which different wavelengths of light hit the surface of the water allowing total internal reflection to come into play.

At the other end of the spectrum is the red light that is filtered out by water rapidly. Beyond the red light there is a part of the spectrum that humans cannot see but can feel. It is infrared. (In the far red.) It is also known as heat. That is the energy that one can feel standing in front of a fireplace even though all the hot air, smoke, and gases are going up the chimney. Heat energy travels at the speed of light. You thought red light had trouble going deep in water.< This description of heat doesn't sit well with me. Heat can come in a variety of different forms. In thermodynamics, heat is simply just energy that is transferred from one part of a system to another, allowing temperatures of a part of a system and it's surroundings to change (forgive me that this doesn't paint the entire picture.) When emitted infrared light is in a vacuum, it does travel at the speed of light and it does carry with it some amount of energy. But if infrared travels in some medium, it loses some of its speed in certain frames of reference. Additionally, heat can travel by convection and conduction, and these modes of heat travel are immensely important in impacting the temperature of different levels of the ocean.

Neon colors do not loose their color like spectrum colors do. This author has video photographed a red stripe on the side of a wet suit turn to black as a diver descended. The stripe could not be seen! On another part of the suit the neon red and "hot pink" still were sending out their bright colors at 100'. That is because they fluoresce. Ultraviolet is found after violet on the spectrum. It is invisible to humans. It, like violet, goes to extreme depths. When a neon color is struck by the invisible ultraviolet it glows or fluoresces.< I think this description of fluorescence will cause readers confusion. It sort of implies that there is some sort of intrinsic difference in "neon color" and "spectrum color." Just for clarity's sake, the only difference between fluorescent and non-fluorescent light is the manner in which that light was emitted. The light from either must still be part of the EM spectrum. The thing about fluorescence is that involves molecules that are able absorb some relatively low wavelength light (invisible or not), become energized, and then reach their electronic ground states by emitting light at a higher wavelength. We will be able to see it if the emitted light falls within the visible light range (assuming you're not colorblind).