Remove User personalisation settings on logoff

I'm setting up Group Policies for to controlling Windows 10 when we roll it out. I'm currently stuck on how to remove user personalisation on logoff.
For example if a user chooses a new color scheme that's OK. However when they log off that color scheme is used for the lock and logon screens for the next user. Once the next user is logged on they get their own color settings.
I want the lock and logon screens to revert back to default Microsoft blue (behind the image*).

*To complicate things slightly I have used group policy to define a custom image for the lock and logon screens. This does work. However if a user chooses a high contrast theme the image is not displayed at all and the high contrast theme is present on the lock and logon screens until the next user logs on.