[LyX/master] Fixup d207e85c: paint sublabel with the correct background color

[Jean-Marc Lasgouttes]

commit 74540c9896892b8f956f52258a59613af83a5cf8
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Mon Feb 24 10:37:14 2020 +0100

    Fixup d207e85c: paint sublabel with the correct background color
    
    The above mentionned patch did paint the background of the sublabel to
    avoid "bold-like" effect. However the correct backgound color is the
    row's one, not the inset's one.
---
 src/insets/InsetCollapsible.cpp |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/insets/InsetCollapsible.cpp b/src/insets/InsetCollapsible.cpp
index 67d19ca..d4c3fd3 100644
--- a/src/insets/InsetCollapsible.cpp
+++ b/src/insets/InsetCollapsible.cpp
@@ -371,7 +371,7 @@ void InsetCollapsible::draw(PainterInfo & pi, int x, int y) const
 			int w = 0;
 			int a = 0;
 			int d = 0;
-			Color const col = pi.full_repaint ? Color_none : pi.backgroundColor(this);
+			Color const col = pi.full_repaint ? Color_none : pi.background_color;
 			theFontMetrics(font).rectText(buttonLabel(bv), w, a, d);
 			int const ww = max(textdim.wid, w);
 			pi.pain.rectText(x + (ww - w) / 2, y + desc + a,