The sun is a ball of incandescent gas. That gas moves about, flowing up and down as well as across the sun’s surface. This movement keeps the sun’s temperature roughly uniform but there are occasionally imperfections; regions of the sun’s surface that get out of balance with the rest of the sun. When you cook a thick soup on the stove, there will also be regions of the surface that are cooler than others.
Light from the sun travels in straight lines (apart from some wave effects called diffraction, that are unimportant in this case). As sunlight passes objects, those objects absorb or scatter the sunlight, leaving regions of space that no longer contain any electromagnetic waves. Regions of space behind the objects contain no sunlight and do not appear illuminated. We perceive those dark, unilluminated regions as shadows.
Brown water contains colored contaminants that provide the color. Brown is the typical end result for a random mixture of pigments. The blue ocean is caused mostly by the sky. Since the ocean reflects some of the light from the sky, it appears blue. Pure water is almost completely colorless. Thus a glass of water has no color (unless you illuminate it with colored light). But if you look at a white light through many meters of water, that light will become slightly colored. Water absorbs a very small amount of visible light and you will see only what is not absorbed. I’m not sure what color pure water has. It may appear slightly green.
Some of them may be polarized materials, blocking horizontally polarized light, but most are simply absorbing materials that are embedded directly in the glass during its manufacture. Chemically tinted glass just darkens the sky be absorbing some of the light passing through the glass, regardless of polarization. It’s not possible to chemically treat the glass to make it absorb only one polarization of light because that treatment would have to carefully align its molecules. In the plastic polarizing sheets, there is an alignment process (usually stretching in one direction) that lines up all the absorbing molecules.
Dark fabrics or surfaces are very good at absorbing and emitting light. That is why they are dark. They must contain electric charges that move fairly easily (making them good antennas) and these charges must be good at exchanging energy with the surrounding material as heat. When light strikes these charges, the charges begin to move and absorb the light’s energy. This energy flows into the material as heat. Since the light is absorbed, the material appears dark (no light is reflected back toward you). But the material will also emit light very effectively when hot. If you heat a black object up, heat will flow into the charges, which will begin to move and will emit light. Thus black objects are good at both absorbing and emitting light.