Looks good.

I wonder if it serves any function?

I thought about the pre painted ones that H-D sells for my Train.

My bike is black denim, and I question if I should use a black denim or gloss black spoiler as the frame is gloss black, but the fenders and tank are denim.

 

It serves no purpose whatsoever other than looking cool. It's purely aesthetic.

Tough to say Cav Cop. It IS next to the gloss black frame, so that would make a sort of sense. However, if the rest of your tins are denim black, it may work to match it up with them.

Up to you.