Manos86 if you go to the home screen page following what the other comment told you to do, it is there below colors and color contrast options. It says icons. Click on it and it will take you to a toggle called themed icons with a "beta" tag.
You can also reach it by Long Press Home screen -> Wallpaper -> Swipe to home screen (the default is lock screen) -> Icons -> Themed Icons (Beta)
It might not be visible if you use some other launcher than the default launcher. In this case you need to use the options the launcher might have for the same.