Switch OEM Theme between Blue and Gold on Honor 8 How can a base theme be switched on Honor 8 device?

A child of my friend somehow managed to switch device theme on his blue device as if it was on gold device. Icons became silver-gold and wallpaper was switched to gold. This gold theme can be seen on images of gold version of Honor 8 in product catalogs. The same for blue theme. See image of two phones in linked article (it is not mine so I only keep it linked).

The side effect of the switch was losing of all custom desktop folders, app icons they are now outside the folders and sorted alphabetically across multiple screens.

No 3rd party theming apps were installed or used, I checked Play Store history which also tracks app usage. At the time of the switch, only one game was used. There was no reboot or similar.

I tried to search for theming in settings, but I found only possibility to switch a wallpaper.

How the entire thing could even happen?
How we can switch from gold back to blue device OEM theme?
After some further research I found that Honor uses Huawei EMUI user interface and it has its own theme switcher app called Theme. It was lost among the apps as they became reordered, easy to get overlooked.

After launching the app, go to tab Me, switch to desired OEM or installed theme and confirm.