Gui: use default app text color for Python code instuctions highlighting

This allows to deal with OS native dark themes
 In such cases, Python instructions were black on a dark background

src/Gui/DlgEditorImp.cpp

@@ -68,7 +68,7 @@ DlgSettingsEditorImp::DlgSettingsEditorImp( QWidget* parent )
 
     d = new DlgSettingsEditorP();
     QColor col;
-    col = Qt::black;
+    col = qApp->palette().windowText().color();
     unsigned int lText = (col.red() << 24) | (col.green() << 16) | (col.blue() << 8);
     d->colormap.push_back(QPair<QString, unsigned int>
         (QString::fromLatin1(QT_TR_NOOP("Text")), lText));

src/Gui/PythonConsole.cpp

@@ -100,7 +100,7 @@ struct PythonConsoleP
         callTipsList = nullptr;
         interactive = false;
         historyFile = QString::fromUtf8((App::Application::getUserAppDataDir() + "PythonHistory.log").c_str());
-        colormap[QLatin1String("Text")] = Qt::black;
+        colormap[QLatin1String("Text")] = qApp->palette().windowText().color();
         colormap[QLatin1String("Bookmark")] = Qt::cyan;
         colormap[QLatin1String("Breakpoint")] = Qt::red;
         colormap[QLatin1String("Keyword")] = Qt::blue;
@@ -932,7 +932,7 @@ void PythonConsole::changeEvent(QEvent *e)
         }
     }
     else if (e->type() == QEvent::StyleChange) {
-        QPalette pal = palette();
+        QPalette pal = qApp->palette();
         QColor color = pal.windowText().color();
         unsigned int text = (color.red() << 24) | (color.green() << 16) | (color.blue() << 8);
         auto value = static_cast<unsigned long>(text);

src/Gui/SyntaxHighlighter.cpp

@@ -22,6 +22,9 @@
 
 #include "PreCompiled.h"
 
+#include <QApplication>
+#include <QPalette>
+
 #include "SyntaxHighlighter.h"
 
 
@@ -33,11 +36,16 @@ class SyntaxHighlighterP
 public:
     SyntaxHighlighterP()
     {
-        cNormalText.setRgb(0, 0, 0); cComment.setRgb(0, 170, 0);
-        cBlockcomment.setRgb(160, 160, 164); cLiteral.setRgb(255, 0, 0);
-        cNumber.setRgb(0, 0, 255); cOperator.setRgb(160, 160, 164);
-        cKeyword.setRgb(0, 0, 255); cClassName.setRgb(255, 170, 0);
-        cDefineName.setRgb(255, 170, 0); cOutput.setRgb(170, 170, 127);
+        cNormalText = qApp->palette().windowText().color();
+        cComment.setRgb(0, 170, 0);
+        cBlockcomment.setRgb(160, 160, 164);
+        cLiteral.setRgb(255, 0, 0);
+        cNumber.setRgb(0, 0, 255);
+        cOperator.setRgb(160, 160, 164);
+        cKeyword.setRgb(0, 0, 255);
+        cClassName.setRgb(255, 170, 0);
+        cDefineName.setRgb(255, 170, 0);
+        cOutput.setRgb(170, 170, 127);
         cError.setRgb(255, 0, 0);
     }
 

src/Gui/TextEdit.cpp

@@ -23,6 +23,7 @@
 #include "PreCompiled.h"
 
 #ifndef _PreComp_
+# include <QApplication>
 # include <QKeyEvent>
 # include <QPainter>
 # include <QRegularExpression>
@@ -197,7 +198,7 @@ struct TextEditorP
     QMap<QString, QColor> colormap; // Color map
     TextEditorP()
     {
-        colormap[QLatin1String("Text")] = Qt::black;
+        colormap[QLatin1String("Text")] = qApp->palette().windowText().color();
         colormap[QLatin1String("Bookmark")] = Qt::cyan;
         colormap[QLatin1String("Breakpoint")] = Qt::red;
         colormap[QLatin1String("Keyword")] = Qt::blue;