The D7200’s auto white balance system is a good failsafe for most conditions, but sometimes it fails to correct enough for warm-toned artificial lighting and sometimes it corrects light that doesn’t need correcting, such as sunsets or the cool, blue colours of dawn.
This is where you need to switch to one of the white balance presets, which you do by pressing and holding this button and turning the rear command dial.
You can also set the white balance in degrees Kelvin, a popular approach amongst professionals, especially when using studio lighting, and you can also measure and set the white balance manually.
Holding the button and turning the front dial applies a correction to the current white balance setting. It’s unlikely you’ll need this – most people looking for that kind of control will shoot RAW files instead, because these allow you to adjust the white balance later.