Photoshop RGB Color mode uses the RGB model, assigning an intensity value to each pixel. In 8‑bits-per-channel images, the intensity values range from 0 (black) to 255 (white) for each of the RGB (red, green, blue) components in a color image. For example, a bright red color has an R value of 246, a G value of 20, and a B value of 50. When the values of all three components are equal, the result is a shade of neutral gray. When the values of all components are 255, the result is pure white; when the values are 0, pure black.
RGB images use three colors, or channels, to reproduce colors on screen. In 8‑bits-per-channel images, the three channels translate to 24 (8 bits x 3 channels) bits of color information per pixel. With 24‑bit images, the three channels can reproduce up to 16.7 million colors per pixel. With 48‑bit (16‑bits-per-channel) and 96‑bit (32‑bits-per-channel) images, even more colors can be reproduced per pixel. In addition to being the default mode for new Photoshop images, the RGB model is used by computer monitors to display colors. This means that when working in color modes other than RGB, such as CMYK, Photoshop converts the CMYK image to RGB for display on screen.
Although RGB is a standard color model, the exact range of colors represented can vary, depending on the application or display device. The RGB Color mode in Photoshop varies according to the working space setting that you specify in the Color Settings dialog box.