Cassidy Sleeves and Some Button Choices
I looked in my button stash and looked at other Cassidys on Ravelry and I think the sweater looks good with buttons that blend and hide OR with buttons that contrast with the yarn used to knit it. (So basically, the choices are wide open here.) My first instinct was to go with a shell button like the one at the bottom (this one is too small, I would get bigger buttons of this type for Cassidy). But then I found the top three buttons and I think they would work too. The top button is a simple brushed metal with "stitching" around the edges. The second button has a dragon on it, and the third button down has three Celtic horses and looks kind of worn or aged. I'm leaning towards the horses because they're not as dark as the dragons. I like shell buttons, but I don't think they're right for this, also, depending on how the light hits them, they can look blue green (great) or yellow brown (not really for this sweater). The top button looks fine, but I don't think it's interesting enough with the cables on this sweater. To me, it would look better on a simpler sweater.
Just a note, I think I got all of these buttons (except the shells) from The Button Drawer and the yarn is not actually sparkley - those are water droplets. I sprayed the sleeves down with water after pinning them before I took the photos. Just in case anyone was wondering.