RGB is a additive, projected light color system. All colors begin with black "darkness" (0,0,0), to which different color "lights" are added to produce visible colors. RGB "maxes" at white (255,255,255), which is the equivalent of having all "lights" on at full brightness (red, green, blue).
Most screens (computer, phone, media player, television, ect) are RGB (e-ink screens being a popular exception). The pixels have tiny subpixels that display varying intensities of red, green and blue.