Gain
Gain adjusts the contribution of an individual color channel. Separate red, green and blue gain controls can change white balance; they do not work in the same way as one overall backlight-brightness setting. The available ranges and their effects depend on the monitor. EIZO's display manual
BetterDisplay can expose hardware RGB gain when the selected controller supplies it. Software channel adjustments are available separately under Image Adjustments.
Because these paths act at different stages, their numbers are not interchangeable. A hardware value need not have the same scale or neutral point as a software percentage. Use each control's own range and reset behavior when comparing them.
See Device Control for hardware controls and RGB for the color channels.