Mixing red and green color
When you ask Google what color you get when red and green are mixed, several of the answers are that the color turns brown. This is only true if a certain red and green are mixed. A green color can be anything from light yellow-green to deep cold turquoise. Same thing with red, everything from orange to almost violet can be called red. The results of mixtures of these different colors become radically different.
As a reference, it can be smart to start from the primary red, a cold red that many would call a rose. the green complementary color is cold green, an emerald green. As it is, there are two colors that have just the right hue for these complementary colors, namely quinacridone rose and phthalo green yellow shade. When these two are mixed with each other, you get a gray (black) color
If the red color were warmer (or the green yellower), the mixture would turn brownish. On the other hand with a cooler red or bluer green the result becomes unclear violet. So the truth is that a mix of green and red will be anything from unclear yellow to dark violet.
If you want to mix a natural green color for a landscape, red color is needed. Traditionally, green color is mixed by: blue + yellow, green + yellow or blue + green, but all these mixtures give clear and fairly bright green color mixtures. If red is added to the mixture, a much wider color choice arises. Red color is used to lower the value of green color, it makes the green darker. Take a photo of a landscape and find the darkest hue among all the green. In most cases, the color will be almost black. To mix such a color, red color is needed.
There are a few different red colors that act as value lowerers for green color. The most common are probably Quinacridone Rose and Alizarin Lake. The red color must be cold (pink).
Phthalo green (YS) + Quinacridone Rose (PV19)
These colors are opposite to each other and together become gray. The green color gradually becomes darker but with the same hue, neither warmer nor colder, only darker. The red color, like all reds, seems colder when darkened.
Phthalo green (YS) + Quinacridone Red (PR209)
Quinacridone Red is a little warmer than the previous red color so the mixture also gets a little warmer. The green color gradually becomes darker and warmer until it turns into a dark brownish color. The red part lacks the violet hue of the previous blend.
Phthalo green (YS) + Pyrrole Orange (PO71)
Pyrrole Orange in this example is significantly warmer. The green color slowly changes to pleasant warm green tones. Then comes a rather dark brown that turns into an orange earth-colored sienna-like color and then becomes unclear yellow.
Phthalo green (YS) + Permanent Orange (PO62)
Now to an orange color, the mixture completely lacks the dark colors. Instead, the green color gradually becomes warmer to turn into a kind of olive green and then unclear warm yellow.
Phthalo green (YS) + Quinacridone pink (PV42)
Just because I tested an orange color, here comes a test with a violet as well. Cold green is the result, in the middle there are different black-violet colors. There are no warm brownish colors at all.
To make a green color darker, and perhaps more natural, red color is usually used. The red color is usually cold, common colors for the purpose are Quinacridone Rose or Alizarin crimson. Other red colors give different results for the green mixture. Try a few different ones and feel free to try brown as well. In the same way that green can be made darker with the help of red, the reverse also works: A red color can be made darker by mixing in a little green.