Color theory is a set of principles used to create color combinations that are harmonious. Color relationships can be visually represented with a color spectrum wrapped onto a circle (color wheel). Color theory does not analyze shades, tints and or tones. It only analyzes the relationships of pure colors.
Here are 3 simplified principles of color theory: According to color theory, Harmonious color combinations can use any 2 colors directly opposite of each other on the color wheel. They can also be any 3 colors spaced equally around the color wheel forming a triangle. Another more scheme is any 4 colors forming a rectangle (2 pairs of colors directly opposite of each other) When these types of relationships take place they are called “color harmonies” or “color schemes”.
Note: when using a color wheel the color schemes remain harmonious regardless of the rotation of the wheel.