Any chance to call the folks throwing the event and ask what they mean?
Summer weight suit, bright shirt, bold tie. Might even go out on a limb and suggest lighter suit colors.
I tried a search on "dress codes" and couldn't come up with anything easier. Love it when "they" invent new standards. Guess we're not part of the Social In Crowd. Otherwise we'd already know these things. Ask me something easy, like what to wear on a bike ride.