Black hose seem to be almost as troublesome as white to many folks, I guess because we're taught that they are both an absence of color. And indeed I don't wear black ones myself, but I do wear really dark charcoal sometimes. I'd think with Royal Stewart I'd look at some greens or blues though.
Have to agree with everyone on the Sipowitz, or 'mission control' as we call it in Houston. But you state it's an 'informal' event, and at least in my lexicon 'informal' and 'tie' don't go together, so just wear the s/s shirt without a tie. Better yet, once you settle on some hose you like, find a shirt that matches/coordinates with them, that can be a smart informal look.