Technically, it's still ro weather for a few more days, although perhaps the season will be extended due to the heat so late in Autumn! The solution, of course, is to encourage people to think 'cool' by wearing cool, serene colours. Think waves, summer grasses, dragonflies, fireflies (hotarubi), flowing patterns in touch with the current season with a calming effect.
As for right now...
I have a blue iromuji kimono, unfortunately not ro but sha, with a 'floppy' dragon obi in shades of blues and greys, with hints of yellow and orange-y red. To minimize the warm effect as much as possible, I'll pair it with a blue or white obijime, and a white obiage. I'd love to get some green-toned khaki accessories, and maybe ones coloured like dried oak leaves.
In the meantime, think fields and grey clouds at dusk! Cool breezes blowing at the end of a hot day as you sit on the front porch with a jar of sake and a tray of momiji manju, waiting for the moon to make an appearance... much nicer feeling than a muggy Tokyo day, isn't it?