IntelĀ® Trace Analyzer 9.1 Update 2 User and Reference Guide
Gradient in the cell color shows that the cell is tagged. A cell is tagged as soon as a single tagged message exists in it. For example, you can see that messages in Process 3 (P3) are tagged:
Messages that do not pass a filter are not accounted for and may result in a smaller matrix when it occurs in empty rows and columns.