Don't forget about gray jackets for summer. In shades from pearl to mid-gray, it is an often overlooked color that complements tan and cream trousers. That is of course the reverse of the more usual summer pairing of a tan jacket with gray trousers, and it is one that is particularly appropriate for wear in city settings, with gray trousers in a complementary shade like the ones worn by the gentleman in the illustration.
Men who already have a reasonable complement of linen and cotton in their closets may want to look at gabardine for their gray jacketing. Tightly woven, gab is no longer considered a summer cloth but it is comfortable for cooler sunny days. Brown and gray gabardine jacketings are seen frequently in illustrations of classic men's clothing and either or both add another texture to an odd jacket wardrobe.
It deserves mention that classic warm weather jackets tended to be solid in color because that was the cloth that was available before the modernization of weaving after 1950 or thereabouts. The tweeds that made up the majority of patterned jackets were too warm-wearing for the season.
The availability of lightweight patterned cloth is much better today but I believe men should still look to solids for the majority of their June through September odd jacket wardrobes. Most of the patterns on the market look to me to be rehashes of cool weather cloth rather than something unique to the season.
And solid gray is a nice option.