I'm going to teach you all how to do this theme for GO Keyboard.
You need to download GO Keyboard - "Purple Neon" or "Pink" theme from Play store.
You need to download the galaxy moustache wallpaper.
Click on the image below & save it in to your phone.
Go to your "GO Keyboard and select "Theme Setting" and apply one of the theme you've download. FYI, it's best if you can use "Purple Neon" theme GO Keyboard for better effect.
Click on the "Theme Setting" again after applying the theme. Click on "Customize Theme". After clicking, Click on "Portrait background". Select the wallpaper from your albums, from there you select the Galaxy Moustache wallpaper.
Click on the transparency setting and set the transparency to your preference.