I was tasked with creating QR codes for certificates (every certificate leads to a unique page for the certificate number on the website, for security and more information since the certificates were small and made to be pretty instead of useful).
We ended up with Level M golden (more like dark yellow) colored QR codes in the corner - using higher error correction is actually detrimental the smaller you go, and backgrounds, embossing or any kind of advanced design would lead to it being very hard to read - it's better to have a plain ugly QR code that is immediately scannable with any device than a pretty one that is unreadable (just imagine your buyers trying to scan the damn thing five times in a row then give up in frustration).
But the client really liked the idea (and the results), and I am still surprised that so many people don't even consider this nowadays...