1/ When I change the letter colour of important messages in Kmail, this change appears in the message list, but after scrolling in the window or upon any mouse click, the color becomes black again. 
2/ This behavior is valid only for already signed as important letters. If I sign a letter important after the colour change, it will be correct.
3/ I tried to clear the old important signs an reassign again, but in this case  colour remained black.
4/ Shutting down Kontact and restart: all important letters are with black characters again, independent of assigned before or after the colour change.

Reproducible: Always