Here's some code to reproduce:

    QColor color("#88112233");
    QJsonValue jsonValue = QJsonValue::fromVariant(color);

    qDebug() << color;
    qDebug() << color.name();
    qDebug() << QVariant(color);
    qDebug() << QVariant(color).toString();
    qDebug() << jsonValue;
 

// Debug output from above code

// QColor(ARGB 0.533333, 0.0666667, 0.133333, 0.2)
// "#112233"
// QVariant(QColor, QColor(ARGB 0.533333, 0.0666667, 0.133333, 0.2) )
// "#112233"
// QJsonValue(string, "#112233") <-- alpha value is missing

// It seems you have to do something manually like convert to rgba qint32 first...

QColor color;
QVariant v(color.rgba());

//Retrieve
QColor color = QColor::fromRgba(v.toUInt());

... but that isn't sufficient if you want to read QColor as a variant into a QJsonValue using QJsonValue::fromVariant()