Why do my theme and color settings reset after a restart?

Check the ownership and permissions of the relevant configuration files in your home directory. If a file is owned by root, your session may let you change the setting without being able to save it, so it reverts later.

First find out which config file the theme tool or desktop environment is using. Change one setting, then check whether that file was updated. If it did not change, look at its permissions and whether it is read-only.

If the settings tool will not save the changes, editing the relevant config file directly can be a workaround. Make a copy first, and be sure you have the right file for the colors or theme you are changing.