The Productivity Target Range option determines how close a user's productivity should get to the target productivity before productivity charts change color.

If the target range is set as 10% and a user's productivity is currently 20% below the target, then his productivity bar chart is red. When that user's productivity falls within 10% of the target, the bar chart will change from red to yellow, indicating the user is close to reaching his goal.

Example:
If a user’s productivity target is set to 10 hours for the month of April and he has worked 8 hours, then the Monthly Productivity Chart shows up in Red as he is 20% less than the target. If the user has worked 9 hours, then the color of the graph changes to yellow as he is now 10% less than the set target and as mentioned in the Productivity target Range.

Note:
This option is available only in Web TimeSheet Project & billing edition, you can find this option in Projects section under Productivity Preferences.