KMail 5.2.1 (from application - KMail Introduction) kmail5 16.04.1-1.1-x86-64 from vendor openSUSE (Tumbleweed-Oss) 20160609 might be similar to https://bugs.kde.org/show_bug.cgi?id=317803 In Configure KMail... dialog > Appearance > Colors change HTML Status Bar Background - No HTML Message to more attention-getting color (orange #ff5500) color shown is grey (default color I think) when KMail starts, the orange color is shown briefly (~1 second), but the notification then changes to the grey color
I can't reproduce it yet.
Created new user and had a similar result ... - No HTML Message has gray background - change color in configuration dialog - gray background remains in message window, but still shows selected color in configuration dialog - closing and re-opening shows gray background - different behavior - the selected color does not show momentarily as initially reported
Problem disappeared. It's now working as expected. Perhaps there was something in openSUSE Tumbleweed 20160623. From this end, the bug can be closed.