Red, yellow, blue. The foundation.
The three colors that cannot be created by mixing other colors. Every other color in the wheel descends from them. On the traditional artist's wheel (RYB), the primaries are red, yellow, and blue.
Digital screens use a different set: red, green, blue (RGB), because they mix light, not pigment. Print uses cyan, magenta, yellow, black (CMYK). Same wheel logic, different primaries depending on the medium.
