At least there are 2 solutions:
1. Use Qt StyleSheet
You must use the "background" property of QMdiSubWindow: title to change the color, and to remove the icon the trick is to pass it an icon with transparent color
from PyQt5 import QtCore, QtGui, QtWidgets
QSS = """
QMdiSubWindow:title{
background: lightgray;
}
"""
def create_icon_by_color(color):
pixmap = QtGui.QPixmap(512, 512)
pixmap.fill(color)
return QtGui.QIcon(pixmap)
class Mywindow(QtWidgets.QMainWindow):
def __init__(self, parent=None):
super(Mywindow, self).__init__(parent)
self.setWindowTitle("Customized style")
self.mdiarea = QtWidgets.QMdiArea()
self.setCentralWidget(self.mdiarea)
self.mdiarea.setWindowTitle("Test")
self.window = QtWidgets.QWidget()
self.window.setMinimumSize(320, 240)
sw = self.mdiarea.addSubWindow(self.window)
sw.setWindowIcon(create_icon_by_color(QtGui.QColor("transparent")))
if __name__ == "__main__":
import sys
app = QtWidgets.QApplication(sys.argv)
app.setStyle("Fusion")
app.setStyleSheet(QSS)
view = Mywindow()
view.show()
sys.exit(app.exec_())

As you can see in my operating system, it has a white color in the middle that is not desired that serves to color the title of the subwindow, maybe in another operating system it does not generate that problem.
2. Use a QProxyStyle
In this case you can modify the style so it should be a more robust solution than the previous one and should not have other styles. For a simple operation I have created a custom QMdiSubWindow.
from PyQt5 import QtCore, QtGui, QtWidgets
def create_icon_by_color(color):
pixmap = QtGui.QPixmap(512, 512)
pixmap.fill(color)
return QtGui.QIcon(pixmap)
class TitleProxyStyle(QtWidgets.QProxyStyle):
def drawComplexControl(self, control, option, painter, widget=None):
if control == QtWidgets.QStyle.CC_TitleBar:
if hasattr(widget, "titleColor"):
color = widget.titleColor
if color.isValid():
option.palette.setBrush(
QtGui.QPalette.Highlight, QtGui.QColor(color)
)
option.icon = create_icon_by_color(QtGui.QColor("transparent"))
super(TitleProxyStyle, self).drawComplexControl(
control, option, painter, widget
)
class MdiSubWindow(QtWidgets.QMdiSubWindow):
def __init__(self, parent=None, flags=QtCore.Qt.Widget):
super(MdiSubWindow, self).__init__(parent, flags)
style = TitleProxyStyle(self.style())
self.setStyle(style)
self._titleColor = QtGui.QColor()
@property
def titleColor(self):
return self._titleColor
@titleColor.setter
def titleColor(self, color):
self._titleColor = color
self.update()
class Mywindow(QtWidgets.QMainWindow):
def __init__(self, parent=None):
super(Mywindow, self).__init__(parent)
self.setWindowTitle("Customized style")
self.mdiarea = QtWidgets.QMdiArea()
self.setCentralWidget(self.mdiarea)
self.mdiarea.setWindowTitle("Test")
self.window = QtWidgets.QWidget()
self.window.setMinimumSize(160, 120)
sw = MdiSubWindow()
sw.setWindowTitle("Test")
sw.titleColor = QtGui.QColor("lightgray")
sw.setWidget(self.window)
self.mdiarea.addSubWindow(sw)
if __name__ == "__main__":
import sys
app = QtWidgets.QApplication(sys.argv)
app.setStyle("Fusion")
view = Mywindow()
view.show()
sys.exit(app.exec_())
