[LyX/master] Fix #13326

[Koji Yokota]

commit 6903b162dde53352c052dcb0b248a82bbbee71c6
Author: Koji Yokota <yokota at lyx.org>
Date:   Thu Jul 30 01:10:23 2026 +0900

    Fix #13326
---
 src/frontends/qt/GuiPrefs.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/frontends/qt/GuiPrefs.cpp b/src/frontends/qt/GuiPrefs.cpp
index 6998430780..8cbe6d4522 100644
--- a/src/frontends/qt/GuiPrefs.cpp
+++ b/src/frontends/qt/GuiPrefs.cpp
@@ -1606,12 +1606,15 @@ void PrefColors::cacheAllThemes()
 	guiApp->setOverrideCursor(QCursor(Qt::WaitCursor));
 	themes_cache_.clear();
 	theme_names_cache_.clear();
+	// back up lcolor since readTheme() and LyXRC::read() change lcolor
+	ColorSet const backup = lcolor;
 	LyXRC dummyrc;
 	for (int id = 0; id < themesLW->count(); ++id) {
 		FileName const fn(fromqstr(theme_fullpaths_[id]));
 		themes_cache_.push_back(readTheme(fn, dummyrc));
 		theme_names_cache_.push_back(themesLW->item(id)->text());
 	}
+	lcolor = backup;
 	guiApp->restoreOverrideCursor();
 }