The color markings in the Work Schedule Calendar have the following meanings:
Blue: Holidays/Time off – based on the global settings/team member time off values
Gray: Nonworking – if in resource calendar from the project that day is nonworking or is an exception
Orange: Assigned – if the resource is assigned in the current project or in other projects saved in Drive 365
Red: Overallocated – if the resource is overallocated in the current project or between projects saved in Drive 365
White: Free – the team member is free to work