For example, red is from the warm half of the color wheel andblueis from the cool half.
They are contrasting colors.
In graphic design and some other fields, we use a looser interpretation.

Dimitri Otis / Getty Images
In design, it’s more about perception and feeling.
Reds and greens are contrasting colors.
The more transitional colors separating two colors, the greater the contrast.
Some of these high contrast, complementary,clashing colorsare quite pleasing.
Vary the shades of additional complementary colors with less contrast.
In a 12-color RGB color wheel.
red, green, and blue are the three primary colors.
The three subtractive colors of cyan, magenta, and yellow are the secondary colors.