Can you try if this is also a problem in the Troubleshoot Mode Thunderbird

See https://support.mozilla.org/en-US/questions/1535478

It looks like this problem has persisted for many years. What I do: 1 Highlight text Select Format --> Text Color... Click Choose a color: (box) Select red on color wheel Close picker See that box color is red, HTML color string is red (#cb0000) Click OK Nothing changes - What I do: 2 Highlight text Select Format --> Text Color... Click Last-picked color (red) Box color doesn't change, but HTML color string is red Nothing changes - What I do: 3 Highlight text Select Format --> Text Color Click Choose a color: (box) Select red in Apple picker Click OK (leave picker open) - What I do: 4 Highlight text Select Format --> Text Color... Type "red" in Enter an HTML color string Click OK Nothing changes