Summerweights

Ahh, the swamp.  D.C. is like no other in this regard.  I wish I could tell you that textile science has solved the problem once and for all, but to my knowledge, sorry.  The thing about summer is that the homogenization of men's suits works against us.  Fabrics best suited for summer (cotton, linen, poplin) look more casual and tend to come in more-casual colors like tan or very light grey (or seersucker's narrow stripes).  Would that we all had the wealth to decamp to the country in the summer, where such suits would be at home.

The question becomes how to dress up inherently casual fabrics.  The answer is, as usual, razor-sharp tailoring, or tailoring at least sharp enough to convey the fact that you have employed it.  The next is consistency with your tie.  Wear something in knit silk, as shown, for example, to show that you recognize that you are wearing a somewhat casual suit, rather than that you only had one suit clean, it was this one, and you wore it out of necessity, then tried to dress it up with ancient madder.  Pocket squares are a must, using either white with the TV fold, as shown, or something that coordinates extremely well with the rest of the outfit.  And wear your best shoes.  Suede if you have them and it's not raining.  Calf otherwise.  Bluchers would best fit our idea of consistency, but then, who these days recognizes their pastoral nature compared to the oxford?

I am convinced that dressing respectfully for the occasion is more a matter of communicating that you have amply prepared for it than of wearing the most formal outfit that the occasion will support.  Exceptions made for black tie, of course.