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Mix red and yellow. Change the hue by altering proportions. Add black or white to change the value.

Article:
Orange is a secondary color, which means that you can make it by combining two primary colors. The two primary colors needed for orange are red and yellow.  "Primary" colors exist naturally and cannot be created by combining other colors. Red, yellow, and blue are the three primary colors, but you'll only need red and yellow to create orange. "Secondary" colors are made by combining two primary colors. Since you need to combine red and yellow to make orange, orange is considered a secondary color. The other two secondary colors are violet and green. Combining equal parts of pure yellow and pure red will create pure orange, but if you'd like a slightly different hue, you can add either more yellow or more red to change it. Yellow-orange and red-orange are the two simplest variations. These colors are also known as "tertiary" colors. Tertiary colors fall evenly between secondary and primary colors on the color wheel.  Yellow-orange consists of two parts yellow and one part red, or one part orange and one part yellow. Red-orange consists of two parts red and one part yellow, or one part orange and one part red. You can lighten or darken orange without changing the hue by adding white or black, respectively.  The amount of white or black you add will determine how much lighter or darker the orange hue becomes. Note that lighter values are typically referred to as "tints," while darker values are commonly referred to as "shades."