The Color Legend in TimeTable Visio allows you color code your schedule based on any activity code (User Field), property, or Resource Assignment you have in your schedule.
The color legend configuration window can be found by clicking on the Color Legend button in the TimeTable Ribbon.
By default, all new projects have None set as their Color Legend. This means all tasks display as white. However, clicking the dropdown will reveal all of the metadata from the schedule that can be used to color code.
Note: The Manual: Responsible option is available for all schedules, and is a way to color code your schedule if it didn't come with any metadata.
If you don't see any options beyond None and Responsible then your schedule likely didn't come with any info.