Black. I hope you have fun!
Seriously, the recentish reappearance of nude hose ( largely do to Kate M.) has not filtered down to the masses yet (us) so I think they will make you look dowdy.

Assuming it is an evening event.....black. Nude if daytime.

Black.

Oh Oh. I had that same issue a couple of weeks ago and wore nude. Slim pencil skirt, silverish top and patent leather high heel shoes.

I think it might be coming from the fact that a lot of young women don't wear nylons anymore. They seem to wear bare legs with highheels. Kate Middleton probably can't do that so is wearing nude nylons.

If you are going to wear nude make sure that they are a really good quality sheer and don't come across looking like support hose.

I had a similar question last year and my "young" friend (age 36) (I'm 49) told me either nude hose or nude legs. No black. I was wearing a black dress and black heels. I tried everything on with nude hose (there was no way I was going with nude legs in March in New England) and I felt like I looked (1) matronly and (2) short. I much prefer the "clean line" of black versus the stripey effect of black dress, beige legs, black shoes.

I think it depends on your region of the country, and what semiformal means there.

Here in the midwest, semiformal would mean men in a suit and women in a dress or skirted suit that is not floor length.

I am almost 50 and would be bare legged unless it was winter. Then I would wear either high quality nude, or black with a pattern to it. And spanks!

Black (try both sheer and semi-sheer) -- to create a vertical line ....