Seems like Qt painting engine don't respect windows theme in some cases. For example all hyperlinks are blue which is not always good for text readability.

Sample code

#include <QApplication>
#include <QWidget>
#include <QVBoxLayout>
#include <QLabel>
#include <QTextEdit>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget w;
w.setLayout(new QVBoxLayout());
QLabel* label = new QLabel("<a href='http://qt.io'>qt.io</a>");
QTextEdit* edit = new QTextEdit("<a href='http://qt.io'>qt.io</a>");
w.layout()->addWidget(label);
w.layout()->addWidget(edit);
w.show();
return a.exec();
}

Just choose any high contrast windows theme and run sample code to reproduce the bug.