[LyX/master] Make latex highlighter colors compatible with dark theme

[Guillaume Munch]

commit c76e0f115336bb5e94bce1a1b9b3312bc682c0c6
Author: Guillaume Munch <g...@lyx.org>
Date:   Tue Jun 14 21:45:47 2016 +0100

    Make latex highlighter colors compatible with dark theme
    
    Partial fix for #8325

diff --git a/src/frontends/qt4/LaTeXHighlighter.cpp 
b/src/frontends/qt4/LaTeXHighlighter.cpp
index 9a9e545..fa949a6 100644
--- a/src/frontends/qt4/LaTeXHighlighter.cpp
+++ b/src/frontends/qt4/LaTeXHighlighter.cpp
@@ -19,13 +19,23 @@
 namespace lyx {
 namespace frontend {
 
+
 LaTeXHighlighter::LaTeXHighlighter(QTextDocument * parent)
        : QSyntaxHighlighter(parent)
 {
-       keywordFormat.setForeground(Qt::darkBlue);
+       auto blend = [](QColor color1, QColor color2) {
+               int r = 0.5 * (color1.red() + color2.red());
+               int g = 0.5 * (color1.green() + color2.green());
+               int b = 0.5 * (color1.blue() + color2.blue());
+               return QColor(r, g, b);
+       };
+       QPalette palette = QPalette();
+       QColor text_color = palette.color(QPalette::Active, QPalette::Text);
+       keywordFormat.setForeground(blend(Qt::blue, text_color));
        keywordFormat.setFontWeight(QFont::Bold);
-       commentFormat.setForeground(Qt::darkGray);
-       mathFormat.setForeground(Qt::red);
+       commentFormat.setForeground(palette.color(QPalette::Disabled,
+                                                 QPalette::Text));
+       mathFormat.setForeground(blend(Qt::red, text_color));
        warningFormat.setForeground(Qt::red);
        warningFormat.setFontWeight(QFont::Bold);
 }