I've done this! You can also cut a small square of diffraction grating and put it on top of a hardening chocolate candy (like an enrobed square of ganache) to make decorate a completed chocolate: http://whoisgood.dog/img/chocolate-diffraction-picture.jpg
Also tip: easiest way to temper a pot of chocolate is with an electric hand-mixer. Wait until it's 32C, mix for fifteen seconds, bam tempered.