It means color gradient. Olive green and navy blue are two different colors. Olive green is as green as leaves. Navy blue describes the gradual change of color. Twelve colors are also called twelve color rings. It refers to twelve different colors. They are red, orange-red, orange, orange-yellow, yellow-green, green, blue-green, blue-purple, purple and purple. Red, yellow and blue play an important role in color matching. They are active in various color combinations, changing each other's lightness, brightness and hue to the maximum extent, and producing multi-level and multi-variety beautiful colors.