Icon size on QComboBox's popup list - c++

Question

I'm trying to make a simple QComboBox with a few color options. The easiest way I found so far was to make a QPixmap for each item, fill it with a color and use it as the item's icon:
this->colorComboBox = new QComboBox;
this->colorComboBox->setIconSize(QSize(100, 15));
QPixmap colorIcon(100, 15);
this->colorList.push_back(QColor(255, 255, 255, 255));
this->colorList.push_back(QColor(194, 169, 160, 255));
this->colorList.push_back(QColor(235, 206, 157, 255));
this->colorList.push_back(QColor(254, 121, 5, 255));
this->colorList.push_back(QColor(255, 195, 78, 255));
this->colorList.push_back(QColor(111, 203, 172, 255));
for(unsigned int i = 0; i < this->colorList.size(); ++i)
{
colorIcon.fill(this->colorList.at(i));
this->colorComboBox->addItem(colorIcon, QString(""));
}
The problem is, even though the color rectangle displays well on the button for the currently selected item:
It's displaying tiny for the items on the popup list:
It seems that the pixmap itself is always scaled down to a width of about 15px, no matter what size I choose for setIconSize.
I feel like this should be really simple to solve, but I've tried several things and nothing seems to work... Thanks in advance for the help.
Edit:
The QSS has the following for QComboBox. I tried changing QComboBox::drop-down's width to 100px and the box itself gets larger, the icon still tiny.
QComboBox
{
border: 1px solid #101010;
background-color: #808080;
color: #d0d0d0;
border-radius: 4px;
selection-color: #f58113;
selection-background-color: #808080;
show-decoration-selected: 0;
}
QComboBox:on
{
padding-top: -10px;
padding-left: 4px;
}
QComboBox::drop-down
{
subcontrol-origin: padding;
subcontrol-position: top right;
width: 15px;
border-left-width: 0px;
border-left-color: #000000;
border-left-style: solid;
border-top-right-radius: 3px;
border-bottom-right-radius: 3px;
}