InLoox reports working days as overbooked (colors yellow, red, and pink) if the effort exceeds the working time. The effort of the assigned tasks is distributed linearly to the working days in this period according to the time frame that InLoox calculates either from the start/end date of the task, assigned task or project.
Example: the task "Create presentation" has an effort of 5 hours. The start date is today at 2 pm and the end date is tomorrow at 10 am. InLoox distributes the effort across today and tomorrow at 2.5 hours each. However, since the working time calendar specifies a working time from 7:00 to 16:00, today is overbooked by 0.5 hours. Today's 2.5 hours can no longer be completed in full within the defined working time, so today is marked in yellow.
InLoox can display and highlight absences in the workload overview with an icon.
In order for that to work, you need to add work-free days to calendars or individual people in the InLoox settings. Read the help article Define working hours, calendars and days off.