One of the features in earlier versions of OS X was that you could change the display color output (or bit depth) in the Displays system preferences. However, in recent versions of OS X Apple has removed this option. If you go to the Displays system preferences you can set the resolution, the brightness for internal and Apple-supplied displays, and rotation and refresh rate options. The colors are now set to be optimal for the display, which means they will default to the highest setting or go to the setting that a particular application requires.
While the color output feature is missing, how many people will honestly miss it? When is the last time you set the color output of your display to anything below the maximum value?
The purpose of color output selections in the past was mainly application compatibility. As color became more of an option for systems in the '80s and '90s, the color palette went from two colors to four, sixteen, two hundred fifty-six, and then thousands and millions as video cards supported 16-bit, 24-bit, and 32-bit color processing. Many older applications were coded for a specific color bit depth, and would require your system to support a specific number of colors in order to work properly.
These days coding conventions make it unnecessary to set specific color bit depths, so having this setting is almost pointless. Apple does offer options in the Universal Access system preferences for setting the system to grayscale, to invert colors, and to enhance contrast, but maximizing the color options on the display will only help enrich the user's experience instead of offering limited colors that blend together in odd dithering patterns to simulate the missing tones and hues.
Despite this, however, there may still be an odd time or two where you might need to set custom color outputs. In these instances, you will need to rely on a third-party tool to enable the settings you need. A couple of these are Display Maestro and SwitchResX, which run as menu options that contain settings for various timings, resolutions, and bit depths. These tools are best for managing unusual monitor setups, but can also be used on standard displays for meeting specific application requirements, if needed.