Here is info form the manual.
All tracks are automatically assigned a color.
• To control which colors are used for new tracks, use the “Auto Track Color Mode” pop-up menu in the Preferences dialog (Editing–Project & Mixer page). The available options are described in the section “Applying track colors automatically” on page 537.
• To change the color for existing tracks, use the Select Colors pop-up menu on the toolbar.
This is described in detail in the section “About the Select Colors pop- up menu” on page 538.
• To change the color for a track you can also press [Ctrl]/[Command], point the mouse at the strip where the track color is shown and click. The color strip is shown, allowing you to select the desired color.
This method works in several places where the track color is visible, i.e. in the track list, the track name field in the Inspector, and the channel name field in the Mixer.
• To override the track color for individual events and parts, use the Color tool or the Select Colors pop-up menu. For more information, see “Coloring tracks, parts, or events manually” on page 538.