semi-formal dress for women in Japan?

I'm going to be studying at a Japanese university for a few months, and I need to wear formal or semi-formal, "appropriate" clothing to a matriculation ceremony. The Japanese students will be wearing suits or Japanese formal wear.

Trouble is, I have no idea what semi-formal

Look at pictures of the ceremony last year or just go with a black dress jacket with a skirt and white blouse. (Black or very dark works both).

Skirt suit (black, navy blue, or gray would do) with a white/beige/light blue blouse, or maybe one-piece dress (knee-length at least) with a dark-colored jacket over it.

If you google with 入学式　(matriculation ceremony) and 大学 (university/college), you will get a whole bunch of images.

Actually, suit shops tell us that it's not "black" but "charcoal" (and sometimes black is kind of too much). But, yes, they all look black.