The color wheel is divided into warm and cool colors.
When a warm color is placed next to a cool color, there is a very strong contrast.
Alternatively, when a cool color is placed next to another cool color (for example, green next to blue) there is a pleasing harmonious effect.
Warm colors: traditionally indicate activity and light.
Cool colors: indicate calm, distant and soothing environments.
White, black and gray are generally considered neutral colors.