zeRGBa is a controller widget for picking colors by mixing red, green, and blue. Each basic color ranges from 0 to 255. The RGB color system constructs all the colors from the combination of the red, green and blue. The red, green, and blue use eight bits each, which have integer values from 0 to 255. This makes 256*256*256=16,777,216 possible colors.
The zeRGBa widget uses three pins on your hardware (Raspberry Pi) for each color channel: red, green, and blue.