Mac: If you spend a lot of time tweaking your display, you may have noticed that El Capitan seems to get rid of advanced options, including native and target gamma adjustment. Thankfully, these settings are just hidden behind a keyboard shortcut.
To get the advanced settings back, head to System Preferences > Display, select the Colour tab, then hold down the Option key while clicking "Calibrate." Doing so brings up a checkbox for "Expert Mode" in the Display Calibrator Assistant. From there, you calibrate just as you've always done.