[LyX/master] Change preedit color settings

[Jürgen Spitzmüller]

Am Donnerstag, dem 09.07.2026 um 17:07 +0200 schrieb Jürgen
Spitzmüller:
> Am Mittwoch, dem 08.07.2026 um 10:06 +0900 schrieb Koji Yokota:
> > I noticed the preview of equations have the same background as the
> > main text, so in colored insets like LyX Comment, they are shown as
> > if in another colored box. Can this be fixed e.g. using the
> > transparency package or else?
> 
> It would need to be fixed in the preview loader which sets the
> background and foreground color of previews to Color_background and
> Color_foreground, respectively. You would need to use the inset
> background color instead, and with transparency, overlay that with
> Color_background.

On a closer look, this small change will cause dvipng to generate
previews with transparent background:

diff --git a/lib/scripts/lyxpreview2bitmap.py
b/lib/scripts/lyxpreview2bitmap.py
index 56314356d1..1542af1663 100755
--- a/lib/scripts/lyxpreview2bitmap.py
+++ b/lib/scripts/lyxpreview2bitmap.py
@@ -393,7 +393,7 @@ def main(argv):
     bg_color = bytes(bg_color, 'ascii')
 
     fg_color_dvipng = make_texcolor(fg_color, False).decode('ascii')
-    bg_color_dvipng = make_texcolor(bg_color, False).decode('ascii')
+    bg_color_dvipng = "Transparent"
 
     # External programs used by the script.
     latex = find_exe_or_terminate(latex or latex_commands)

pdftocairo (the PDF chain) does (should) already produce transparent
background.


However, the previews are still displayed with the workarea background.
If the generated pngs are inserted via inset graphics, on the other
hand, the background is correctly transparent.

So there seems to be some transparency support missing in the
PreviewLoader chain, as opposed to InsetGraphics.

Hope this helps,
-- 
Jürgen