In the timing window of PlanAhead tool, if there are any timing violations the item is highlighted in red color. However, the timing window is only highlighting setup and hold violations (i.e., in red color).
Please see the screenshots in the Solution section for an example.
In above screenshots, you can see that MAXSKEW is not highlighted, though the constraint has violations.
The numbers associated with the failing constraint are correct and the failing constraint is correctly highlighted, but the constraint category (MAXSKEW) is not highlighted.
This highlighting issue has been fixed in the Vivado Integrated Design Environment.