There are three primary colors (red, yellow, blue) and three secondary colors (orange, green, and purple). The primary colors are the colors that cannot be made by mixing any other colors, and the secondary colors are made by mixing two primaries together. Red combined with yellow makes orange, yellow combined with blue makes green, and blue combined with red makes purple.
These six colors often appear together on a color wheel in this order: red, orange, yellow, green, blue, purple (then back to red). This places the warm colors (red, orange and yellow) on one side of the wheel, and the cool colors (green, blue and purple) on the other side of the color wheel. This also places the secondary colors in between the two colors that were used to create them. Colors found opposite each other on the color wheel are known as complimentary colors. Complimentary colors are known to be "opposites"--as different from each other as black is from white. Complimentary colors stand out against each other and are often used together for basic graphic designs.
Through the color theory system, different colors are known to achieve different effects. Different colors may draw the viewers in, lead the eye of the viewer around on the surface of the object or image, and create different emotional responses.