Since white and black are not colors, but a neutrals, these can be used to enhance all the other colors, allowing complete freedom to create every other color that there is.
Green is the main color of things living in most natural settings. It soothes one's psyche. Green comes in so many different shades, from softest baby blanket green, to lime green, and the deepest green that is the color of the darkest pine in the forest.
Blue is also a refreshing and pleasing color that has an endless variety of shades and hues, that encompass the water in the oceans, lakes and waterfalls as well as the skies, where it can be deep blue to almost white, depending on your perspective and the angle from which you are looking at things.
Red is a vibrant color. It can stand for power, or in it's more subdued tones, it can be as soft as the pink on the nose of an albino white cat.
For my picture, I would create a beautiful waterfall that empties into a glorious lake, with mountain pines and meadows that are filled with lovely wildflowers, and since white really isn't considered a color, there would also be plenty of opportunity to soften the shades of every color, and blend these three colors together in varying strengths, as well as with the white, to get about every color of the rainbow that also is in my picture.
The rainbow is caused by the abundant spray from the waterfall, and it challenges anything man can create.
You plinky folks should have said to choose four colors. That's really all the primary colors anyway. With these four primary colors, one can make every other color, having the full spectrum, thereby allowing comp;ete freedom to design and create every hue there is, without adding actual metals such as silver or gold.