RBG uses three numbers, each of whose 256 values range from 0-255 to represent the color of each pixel
Red has an opposite color called cyan (blue green). If you reduce red in an image, you increase cyan, and vice versa
Green has an opposite color, a reddish purple called magenta. If you reduce green, you increase magenta, and vice versa.
Blue has an opposite color, yellow. If you reduce blue, you increase yellow, and vice versa.
These conclusions are important to the photographer, because it is rare for the color balance captured by the camera to be perfect. When you go to make color corrections, you need to understand the impact of each change, and learn to tread softly.