demo code(then move two dock into a single group), the two color issue is shown in the attachment:

 # coding: utf-8

import sys
import platform

from PySide6.QtWidgets import QApplication, QMainWindow, QDockWidget, QTextEdit
from PySide6.QtCore import Qt, QSysInfo

def main():
app: QApplication = QApplication(sys.argv)
window = QMainWindow()
dock1 = QDockWidget("dock1")
dock2 = QDockWidget("dock2")
for dock in [dock1, dock2]:
dock.setFeatures(dock.DockWidgetFloatable | dock.DockWidgetMovable)
window.addDockWidget(Qt.LeftDockWidgetArea, dock1)
window.addDockWidget(Qt.RightDockWidgetArea, dock2)

os_info = QTextEdit()
os_info.setText(platform.version())
dock1.setWidget(os_info)

qt_info = QTextEdit()
info = QSysInfo()
qt_info.setText(f"

{info.kernelVersion()}

,

{info.prettyProductName()}

,

{info.productVersion()}

")
dock2.setWidget(qt_info)

window.show()
app.exec()

if _name_ == '_main_':
main()