As much I like circles and blue, I don't feel strongly either way. Most of my Mac icons are not round (Calibre isn't round), so I don't feel a need for a round Sigil icon. Also, my desktop background is blue (did I mention that I like blue?
), so the current maroon icon pops just fine, and a blue icon would actually make it harder to find.
ETA: I just realized there's a whole second page to this thread that I missed when I wrote this post. Looking at all the examples, I'm now leaning toward keeping the current icon unchanged, but I don't think I can change my vote (which was "Don't care").