Apple Color makes extensive use of your system’s onboard graphics card, which can cause odd problems. For instance, if you have a custom color calibration applied to your monitor, the video preview may vanish, leaving a black empty space instead of an image.

To work around this bug, do the following:

1. Exit Apple Color
2. Using System Preferences / Displays, turn off custom color calibration by selecting the top, default calibration
3. Re-launch Apple Color
4. Re-select your custom calibration

As long as Color has already been started, it’s safe to turn the calibration back on.