QCustomPlot has is own layout so you can't use the setStyleSheet...
Here's the code snippet we used to change the graph color to black & white(light grey) :
void AbstractCustomPlot::setTheme(bool isLite)
{
QColor accentColor;
QColor themeColor;
QColor themeBackgroundColor;
QColor traceColor;
if (!isLite) {
accentColor = QColor(78, 156, 207);
traceColor = accentColor;
themeColor = QColor(Qt::gray);
themeBackgroundColor = QColor(48,47,47);
}
else{
accentColor = QColor(Qt::darkBlue);
traceColor = accentColor;
themeColor = QColor(Qt::black);
themeBackgroundColor = QColor(Qt::white);
}
foreach(QCPAxisRect* rect, axisRects()){
foreach(QCPAxis* axis, rect->axes()){
axis->setLabelColor(themeColor);
axis->setBasePen(QPen(themeColor, 1));
axis->setTickPen(QPen(themeColor, 1));
axis->setSubTickPen(QPen(themeColor, 1));
axis->setTickLabelColor(themeColor);
axis->grid()->setPen(QPen(themeColor, 0.5, Qt::DotLine));
axis->grid()->setSubGridVisible(false);
axis->setSelectedTickLabelColor(accentColor);
axis->setSelectedLabelColor(accentColor);
axis->setSelectedBasePen(QPen(accentColor, 1));
axis->setSelectedSubTickPen(QPen(accentColor, 1));
axis->setSelectedTickPen(QPen(accentColor, 1));
}
}
setBackground(QBrush(themeBackgroundColor));
replotNow();
}
Hope it will help !