Hello,
You can try the following steps to troubleshoot this issue:
First check that the "High Contrast" mode is turned off. Navigate to Settings > Easy of access > High Contrast. If the option has turned off, try turning on and then turning off again. Then restart the Server.
Also confirm that the account sync setting is not enabled on the Server, which may result in synchronizing high-contrast mode with other devices. Turn off sync Settings temporarily to avoid interference with Settings on other devices.
I hope this helps. Please let me know if you require further assistance or have any questions.
Best regards