Originally Posted by LonelyNinja
That's possible, but then again it's possible that additional Sharingans only give power to Uchiha. Kind of like a genetic perk.
It's a likely reason, but there are still other ways that we don't know about. Probably. It's a slippery subject.
It's definitely something that's implied and interpreted. As for Sasuke's eyes being different looking, so far every revealed Mangekyou has been different than someone else's, just like fingerprints.
Sasuke didn't technically kill his brother, though. Itachi just fell over from some other ailment. So I'm thinking that you get the Mangekyou from the death of someone close to you, not necessarily by your own hand. There's also intense training, as shown by Madara and his brother. So there are different ways to obtain the Mangekyou Sharingan, we just don't know how some people got theirs.
That's the leading proof we have right now of how Kakashi obtained his MS.