Red is a primary color (red, blue, yellow), meaning it's a specific hue that doesn't happen with mixing of other hues. Green is a mix of other two colors (yellow and blue) and for that reason is a strong competitor with red. Red and green enhance each other, and are referred to as complimentary colors on a color wheel. Complementary colors are pairs of colors which, when combined in the right proportions, produce white or black. When placed next to each other, they create the strongest contrast and reinforce each other.