In the photograph, Nicholas Antongiavanni, author of The Suit: A Machiavellian Approach to Men's Style, on holiday in the Bay area this week. He is wearing a yellow knit tie with his blue and yellow checked linen shirt as well as a navy linen jacket, white bucks, and white flannel trousers.
To the best of my knowledge, cloth for white flannel trousers in anything less than a too-warm-for-summer 17 ounce/500 gram weight can be obtained only from Dormeuil (not Harrison's, as I wrote in the initial version of this post).
The yellow knit necktie, on the other hand, is fairly widely available and one of the classics of summer. It adds a bit of sunshine to a blue blazer, and we are all the better for it.