[comctl32] Regression Background Colour is displayed grey but should be white (where no text is) in setup wizard of Antivir

0.4.9-dev-787-g7673837 gcc dbg
"Avira Antivir Personal 6.35.00.243" from http://www.oldversion.com/windows/avira-antivir-6-35-00-243

We have a regression in comctl32 that was introduced with SVN74136 comctl32/propsheet hbelusca

ThirdScreenOfSetupShowsGreyBackGroundErronouslyWhereNoTextIs.png
Most of that screen should be white.

It has to look like in xp.png

backgroundcolor-regressiontest.txt points to 2 interesting commits in comctl32, both from hbelusca:
-SVN74136 which broke it
-0.4.8-dev-56-g11049bd which already fixed part of it again, see CORE-13929

Please watch these videos carefully:
r73441-ok.webm
r74136.webm most broken
0.4.8-dev-56-g11049bd_untilCurrentHead_greyBackgroundErronouslyThatShouldBeWhite.webm

The videos show multiple issues, some of them can be fixed by enforcing a repaint (moving on and off screen). For example the wrong background in the header sections and the initially not painted pictures in the header section. Those issues are not part of this ticket.

The ticket is solely about the wrong background colour that is grey and should be white, and this issue can not be fixed by an enforced repaint