Color theory encompasses a multitude of definitions, concepts and design applications - enough to fill several encyclopedias. However, there are three basic categories of color theory that are logical and useful : The color wheel, color harmony, and the context of how colors are used.
The first color wheel was designed by Sir Isaac Newton in 1666 so it absolutely predates your introduction to it in kindergarten. Artists and designers still use it to develop color harmonies, mixing and palettes.
The color wheel consists of three primary colors (red, yellow, blue), three secondary colors (colors created when primary colors are mixed: green, orange, purple) and six tertiary colors (colors made from primary and secondary colors, such as blue-green or red-violet).
Draw a line through the center of the wheel, and you’ll separate the warm colors (reds, oranges, yellows) from cool colors (blues, greens, purples).