HWMonitor red CPU

[dasdf]

This is probably a very easy question, but I searched the forum and tried to google the information and did not find a solution:

Why is one of my CPU temperatures highlighted in red? And why is it changing (sometimes CPU4, now CPU 3)...
I've attached a picture

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Thanks in advance for your help

Dasdf

 

[Eightplant]

If you quit HWMonitor and launch it again they'll all be black. I believe the red to be an indicator that at some point while HWMonitor was running, there was a high temp event.