I would like to change the white background (theme)on my infinix note 5 but can't find it in setting. The apps look like they're pasted on a white paper on home page.
Welcome to Android Central! Are you talking about the App Drawer or the homescreen? If it's the homescreen, you probably have to long-press any empty part and tap Wallpaper, then select a different wallpaper. If it's the App Drawer, then most phones don't give you an option to change that in the stock launcher. You could install a 3rd party launcher like Nova, which does give you that option (and more).