When blue and yellow are combined, green is the result. Red, blue and yellow are known as primary colors. These are the three colors that can't be produced by mixing any other colors.
All the colors of the rainbow can be made using the primary colors, plus black and white.
Green is a secondary color. Secondary colors are those that can be produced from mixing two of the primary colors together. Orange and violet are two other secondary colors. The hues of secondary colors are halfway between the two primary colors that produce them.
The relationships between colors is displayed using a color wheel.