-- Put this into custom.lua in your T:A config folder
local current_gamma = 2.2
local gamma_low = false

function gammaPlus()
    current_gamma = current_gamma + 0.1
    gamma(current_gamma)
end

function gammaMinus()
    current_gamma = current_gamma - 0.1
    gamma(current_gamma)
end

function gammaToggle()
    current_gamma = gamma_low and current_gamma + 1.2 or current_gamma - 1.2
    gamma_low = not gamma_low
    gamma(current_gamma)
end

bindKey("B", Input.PRESSED, gammaMinus)
bindKey("B", Input.REPEAT, gammaMinus)
bindKey("N", Input.PRESSED, gammaPlus)
bindKey("N", Input.REPEAT, gammaPlus)
bindKey("M", Input.PRESSED, gammaToggle)