Fix display of colors in labels of arguments.

We need to handle this specially, just as we do the main font.

src/insets/InsetArgument.cpp

@@ -257,6 +257,13 @@ FontInfo InsetArgument::getLabelfont() const
 }
 
 
+ColorCode InsetArgument::labelColor() const {
+	if (labelfont_.color() != Color_inherit)
+		return labelfont_.color();
+	return InsetCollapsable::labelColor();
+}
+
+
 InsetLayout::InsetDecoration InsetArgument::decoration() const
 {
 	InsetLayout::InsetDecoration dec = getLayout().decoration();

src/insets/InsetArgument.h

@@ -77,6 +77,8 @@ public:
 	///
 	FontInfo getLabelfont() const;
 	///
+	ColorCode labelColor() const;
+	///
 	void setButtonLabel();
 	//@}