Merle is a genetic pattern that can be in a dog's coat. Merle comes in different colors and patterns and can affect all coat colors. The merle gene creates mottled patches of color in a solid or piebald coat, blue or odd-colored eyes, and can affect skin pigment as well. There are two general types of colored patches that will appear in a merle coat: liver (red merle) and black (blue merle). They are by far the most desirable pattern.