How can I search MagicCards.info for an exact color identity match?
When you search ci:gur on magiccards.info, you are looking for cards that match that color identity, i.e. that are legal in a deck with whose commander has a GUR color identity, including artifacts. When you append the m, it appears to search for cards that have more than one of those colors in their color identity.

So, in that context, when you are looking for a GUR commander, you are really looking for a card that matches that color identity, but does not match any subset of that color identity.. You can express that using the negation syntax to filter out those sub-combinations, like -ci:ru. The final search is t:creature t:legendary ci:gur -ci:gu -ci:ur -ci:gr. This results in a total of six creatures that have that exact color identity.



I created a Chrome extension to help construct that search automatically. I also recently discovered EDHREC, a site with similar search functionality.