Because of this process, and due to that fact that the signals to the brain determine the color of an object, we could say that things in themselves do not have color. If this is the case then there can be no objective colors. The point is that seeing color is a personal and individualistic experience. The process of being an artist is making yourself aware of color and this awareness can only be achieved through training and practice. One of the most important aspects of color in painting is to understand complementary colors.
Complementary colors are opposite colors and are very important when mixing colors for painting.
Green and red are complementary colors. They are opposites in the sense that they are diagonally opposed in the color wheel. This means, practically, that they tend to react against each other if put side by side. Try this exercise as a first experiment in color. Paint a red rectangle on a piece of paper.