In this photo - shared earlier by Abel - he paired one with his beloved Speedy, sunglasses and LV traveling trunk. 
I know that this particular hat came from Lock & Co - he mentioned it in his post. I’m not sure which line it’s from - not current - but looks to be either straw or sisal and a spectacular aubergine color - perhaps a Homburg style Pork Pie.
Here are a few of my photos on which Captain commented - these watches will now always be associated with him when I wear. 



Whenever I visit Lock & Co (which is often) along with the hats they made and have on display for Admiral Lord Nelson, Winston Churchill, Anthony Eden and Douglas Fairbanks I’ll always picture Captain’s hat in my mind - and tip mine in salute.