Correspondence between color mixing and vertical directions

Marsh
The most prominent feature of the Marsh is the vivid colors of the different pools. Colored water acts on light as a colored filter, and therefore mixing colored waters results in mixing the colors according to the subtractive color model. In the Marsh, this subtractive mixing is associated to the downward direction, while additive mixing is associated to the upward direction.

Second Moving Platform
An illustration of this principle is the puzzle of the second moving platform, which features black, red, magenta, and blue monominoes. Of course, these colors correspond to nearby tiles on the platforms and to the color of water in the pools next to these platforms, but this last explanation doesn't work for the black tile. In the puzzle, Red is on the right, Blue on the left, Black at the bottom and Magenta on top. Red and Blue are opposing on an horizontal axis, and are primary colors in the additive system (it's interesting to note that the third primary color, Green, is not used and is the natural color of water in the Marsh). If you add Red and Blue in the additive system, you get Magenta (on top). But if you subtract them you get Black (at the bottom).

Blue-outlined polyominoes
Another use of the concept is the fact that blue-outlined polyominoes represent underwater areas, and Blue is the color opposing the Yellow of the filled polyominoes in all color models. Subtracting Blue from Yellow therefore gives Black, which explains why Blue is used to represent underwater rooms; as the color of the wires in these rooms; and as the color of the water in the pool where there is the entrance of the first underwater room that we can enter. Conversely, Yellow is the color used above the surface of water (in the platform tiles and for the wires).

Greenhouse
To do

Symmetry Island
To do: can we apply the principle in Symmetry Island, too?