[vogella]

After a theme switch, CSSSWTColorHelper skipped setting a control's new background whenever the parent already had the same color, because getBackground() also reports inherited colors. The reset control then owned no color, and children of a Forms Section painted the Section's title gradient image instead, for example the white text fields in the PDE manifest editor after switching from Light to Dark. The helper now remembers the color it applied and only skips when the control really owns it, and the element resets clear colors through the helper. The existing optimization for unchanged colors stays in place for ordinary re-applies, and a regression test covers the reset case.

[github-actions]

Test Results

   867 files     867 suites   50m 1s ⏱️
 8 548 tests  8 308 ✅ 240 💤 0 ❌
21 516 runs  20 840 ✅ 676 💤 0 ❌

Results for commit 8510b6e.

♻️ This comment has been updated with latest results.

[vogella]

How to reproduce:
The shipped themes use a flat Section title bar, and since e199306 a flat title bar creates no gradient image, so reproducing needs two themes with a real gradient.

Theme B, on top of the Dark theme CSS (e4-dark_win.css on Windows):

#org-eclipse-e4-ui-compatibility-editor Section {
	background-color: #283040;
	background-color-titlebar: #c00000;
	background-color-gradient-titlebar: #0000c0;
	swt-background-mode: force;
}
#org-eclipse-e4-ui-compatibility-editor Section > Composite {
	background-color: #283040;
	swt-background-mode: force;
}
#org-eclipse-e4-ui-compatibility-editor Section Text,
#org-eclipse-e4-ui-compatibility-editor Section Label {
	background-color: #283040;
}

Theme A is the same with #3a2840 for Section > Composite and #006000 for Section Text, Section Label.
The id prefix is needed, otherwise the Dark theme's background-color: inherit on Section wins.

Steps: open a MANIFEST.MF in the plug-in manifest editor on the Overview page, then switch Dark, A, B.
Without the fix, the General Information text fields in B show the red to blue title gradient; with the fix they stay flat #283040.