So I found how to do it, here is my code to change all the colors of a plot exept for data lines :
foreach(QCustomPlot *widget ,PlotList) {
widget->xAxis->setTickLabelColor(colcode);
widget->xAxis->setBasePen(QPen(colcode));
widget->xAxis->setLabelColor(colcode);
widget->xAxis->setTickPen(QPen(colcode));
widget->xAxis->setSubTickPen(QPen(colcode));
widget->xAxis->grid()->setPen(QPen(colcode));
widget->xAxis->grid()->setSubGridPen(QPen(colcode));
widget->xAxis2->setTickLabelColor(colcode);
widget->xAxis2->setBasePen(QPen(colcode));
widget->xAxis2->setLabelColor(colcode);
widget->xAxis2->setTickPen(QPen(colcode));
widget->xAxis2->setSubTickPen(QPen(colcode));
widget->yAxis->setTickLabelColor(colcode);
widget->yAxis->setBasePen(QPen(colcode));
widget->yAxis->setLabelColor(colcode);
widget->yAxis->setTickPen(QPen(colcode));
widget->yAxis->setSubTickPen(QPen(colcode));
widget->yAxis->grid()->setPen(QPen(colcode));
widget->yAxis->grid()->setSubGridPen(QPen(colcode));
widget->yAxis2->setTickLabelColor(colcode);
widget->yAxis2->setBasePen(QPen(colcode));
widget->yAxis2->setLabelColor(colcode);
widget->yAxis2->setTickPen(QPen(colcode));
widget->yAxis2->setSubTickPen(QPen(colcode));
widget->replot();
}