QPushButton come out fended and I did not set that - c++

Question

I'm working in ubuntu kde 20.04, qt5.15
I my purpose was to create a QPushButton that change his color when he got clicked, then I created a new derived class for doing this (Facelet), it works but the colors I got are not those I was assuming to get.
Facelet.h
#ifndef FACELET_H
#define FACELET_H
#include <QPushButton>
class Facelet : public QPushButton
{
Q_OBJECT
public:
explicit Facelet(QWidget * parent = nullptr);
explicit Facelet(int color, QWidget *pareny = nullptr);
void reset();
static QString colors[6];
private slots:
void __change_color();
private:
int _ColorIndex;
};
#endif // FACELET_H
Facelet.cpp
#include "Facelet.h"
QString Facelet::colors[6] = { "background-color: yellow;", "background-color: red;", "background-color: green;", "background-color: rgb(255, 130, 50);", "background-color: blue;", "background-color: white;" };
enum { rxyellow, rxred, rxgreen, rxorange, rxblue, rxwhite };
//public
Facelet::Facelet(QWidget *parent) :
QPushButton(parent),
_ColorIndex(-1)
{
this->resize(75, 75);
this->setStyleSheet("background-color: gray");
connect(this, SIGNAL(clicked()), SLOT(__change_color()));
}
Facelet::Facelet(int color, QWidget* parent) :
QPushButton(parent),
_ColorIndex(color)
{
this->resize(75, 75);
this->setStyleSheet(colors[_ColorIndex]);
connect(this, SIGNAL(clicked()), SLOT(__change_color()));
}
void Facelet::reset() {
this->setStyleSheet("background-color: gray");
}
//private
void Facelet::__change_color() {
_ColorIndex = (_ColorIndex >= 5 ) ? 0 : (_ColorIndex + 1);
this->setStyleSheet(colors[_ColorIndex]);
}
And here my main.cpp
#include <QApplication>
#include <QMainWindow>
#include "Facelet.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QMainWindow w;
Facelet f;
w.setCentralWidget(&f);
w.show();
return a.exec();
}
See? The screen is faded, I want a uniform strong color. What's wrong with my code?

Answer 1

To correct that I found two solution via reimplementation od paintEvent method.
first
void Facelet::paintEvent(QPaintEvent*) {
QPainter p(this);
p.setOpacity(1.0);
}
the first one is pretty easy, reading some topic I found out that a QWidget to have a setStyleSheet(QString) methods working properly need the following line in the paintEvent(QPaintEvent*) method as the official documentation says
void Facelet::paintEvent(QPaintEvent *) {
QStyleOption opt;
opt.init(this);
QPainter p(this);
style()->drawPrimitive(QStyle::PE_Widget, &opt, &p, this);
}