Thanks - it was a "senior moment" or, more likely, a "senior long time"

I'm having a senior moment and just can't remember, or find out, how to change the sorting order apart from clicking on "From", "Subject" etc near the top of the window.
The pop-up menu when I right click doesn't offer sorting methods.
How do I get it to sort by colour (or color for those living on the west of the pond) ?

Bob

When you have a folder open and in foreground look up top in the Folder menu where you set your preference and it will be remembered. The sort order may be different for different Folders.