Color theme file must be named like theme-<color>
All i18n files must contain a new property called: Settings.personalize.theme.theme-<color>
These color themes just change some foregrounds and backgrounds to make NextReports Server having the same chromatic as you desire.
There are also two images that are taken into account.
First is the actions image which is used in popups to decorate the actions menu and which you can define in theme files:
Second image is the Ok image used inside table columns when everything is as should be. This is not defined inside theme files. You just make sure that an image with name tick_<name of theme>