If you decide to host your colored coins metadata on your website, you can include a custom URL when issuing your colored coins. This custom URL must be small enough to fit in the transaction (current limit of 40 bytes for all the OP_RETURN, which means you need to provide a URL with a maximum of approximately 26 characters. This limit includes the characters for 'http://' or 'https://').
If your website domain is too long, we would recommend using a URL shortener to add a shorter URL which links to your website. Please also keep in mind you can let Coinprism provide you with a unique custom URL (of the form: https://cpr.sm/c7kacbIXe5w).