In case you're totally clueless about keyboard decals let me tell you a little bit about these ones. They come on a sheet approximately the size of your keyboard. It is not a silicone cover, they are individual pieces. The decals come cut exactly the size of your keys so you don't have to trim them but you do have to take your time and apply them one by one, carefully so they're not crooked. They're just like stickers and they claim to come off clean without any residue but I can't speak for that as I've never tried to take mine off.
The seller I bought them from is no longer in business (at least not under the same name) but you can still find these same exact stickers in a variety of places. You can find them here on amazon. Or on etsy - all you have to do is search with the keywords "rainbow keyboard decal" under all items or just "keyboard decal" if you'd like different colors.