Every monitor you use with your Mac, be it a built-in one or an external one, will have different color output properties. For example, in one monitor you might see more red than another monitor, which may cause color balances to be off either between two monitors you use with the same Mac, or when you view an image on a different Mac.
To adjust for this, manufacturers generally include color matching profiles for their devices, which act as a color translation filters that slightly adjust output to match industry standards. In this way, a monitor that naturally outputs more red than another will be filtered to have this red dialed back when output is displayed.
The color matching technology in OS X is called ColorSync, and each color-handling device attached to the system is assigned a ColorSync profile. This profile can be a specific one for the device, or more often may be a generic one that applies best to the type of technology the device uses. For instance, an unknown LCD monitor will likely use a standard “Color LCD” profile, which will get a basic LCD monitor’s colors to be “about right” but not always a spot-on match to the intended colors of the system.
If your monitor’s manufacturer provides a color profile, then you can install this to better match colors; however, even this will only be a closer match and not necessarily provide the best color handling since it was created in different lighting and with different hardware settings (brightness, contrast, RGB balance, etc.) on your monitor.
If you wish to have the most accurate color response for your monitor, then I recommend you create your own color matching profile. This will be the best for handling your specific monitor’s output in the lighting you use around your system.
The second is to use a software-only approach to color calibration, which instead of using a colorimeter device for adjustment, has you use your eyes (perhaps the best colorimeter of all) to provide feedback and adjustment. The drawback here is that your interpretation of colors will be more subjective and prone to use error, but with a little practice you can get it right and create very accurate color profiles for your monitors.
One such color calibration package is SuperCal by bergdesign, which offers an in-depth routine for creating full and very accurate profiles for your monitor. This is the approach I recommended for calibrating your monitor, as I have found it to be very consistent, thorough, and very accurate. It is a shareware program, but with a license for all features costing $19 it can be far more economical than a hardware calibrator.
If you do not have a budget for any third-party software or hardware, but would still like to calibrate your monitors, then you can use Apple’s built-in color calibrator. While this runs on the same principles as SuperCal to create color calibration curves, it is a somewhat cumbersome approach that requires squinting and very subjective assessment of color pattern matching. While you can get a decent color profile using this routine (and one that is far better than any generic profile), it is still subject to a little more error on your part:
- Disable any third-party color adjustment programs like Flux or ScreenShade.
- Open the Displays system preferences and click the Color tab
- Click the “Calibrate…” button
- Check “Expert Mode” in the calibrator assistant that pops up
- Follow the on-screen instructions through each step to match the patterns on screen, by changing the contrast and color sliders so the series of Apple symbols disappear into their respective backgrounds.
- When done, save the profile, and then select it for use with your display.
- Do this for every monitor you use with your system (built-in and external).
This process can be repeated for your monitor as many times as you want. Since it is a relatively subjective approach, I recommend you do this several times and then compare each profile you have created. If any one shows vastly different output than the others, then you might have made a mistake somewhere, and can delete that profile. Then you can select from the remaining to use.
The overall goals here are to get a color profile that gives you proper colors by eye (ie, blues do not appear purple or green), and then have colors match across different devices you use. Once you have achieved this to your satisfaction, then you have calibrated your monitor.