It's possible that this has already been discussed, but I recently noticed something interesting about the colors of Susanoo. Itachi's Susanoo is red, Madara's is blue, and Sasuke's is a combination of both colors, resulting in purple. I believe this may symbolize the balance between good and evil that Sasuke grapples with. However, it's also possible that the creators simply thought a purple Susanoo looked cool, so I might be overthinking it.