Hue is how a color is perceived to be redRed is the first of three primary colors in an additive color model. The "R" in RGB. More, yellowOne of the three primary colors in a subtractive color model. The "Y" in CMYK. More, greenGreen is the second of three primary colors in an additive color model. The "G" in RGB. More, blueBlue is the third of three primary colors in an additive color model. The "B" in RGB. More, purple, etc. The attribute of color is measured in degrees on the diameter of a color wheelA color wheel is a diagram representing the visual spectrum of colors. More.