At my aunts funeral, me and my dad sat together for most of the time. It was a protestant service, my first, (I'm a Catholic) so I wasn't sure how much differently it worked. We sat there forever waiting for the pastor to show up and begin the service, so long that I finally turned to my dad and asked if he thought there was even going to be a service. He turns and looks at me with this half smirk on his face and says "I'm not sure, but there's suppose to be fire works in half an hour". For some reason, me and my father cant escape our sense of humor even in the most morbid circumstances. Needless to say, I got some weird looks.
But anyways, wearing all black to a funeral is fine. As already said, it shows respect for the deceased.