One of the features I use regularly in the display settings of OS X is the adjustment of the gamma setting of my monitor. This is useful because it can lighten up dark movies when you are watching them on your Mac. The gamma setting is only available in the “expert” mode of display settings which has disappeared in El Capitan. Thankfully expert mode is still there, it’s just hidden. To get into expert mode on El Capitan hold down the option key when you select ‘Calibrate…’ in display settings.
This is what you see when you open ‘Displays’ in your System Preferences in OS X. If you hold down the option key while you select ‘Calibrate…’ the box to select the hidden expert mode from previous versions of OS X will appear.
Now you can click in the expert mode box which will enable you to set the gamma settings.
You can use this setting to make dark movies appear brighter when you watch them on your Mac, although you will want to change the gamma settings back for normal work.