If you google cavalry hats, all searches refer you to the black hats -- however -- in the old days, only the officers were allowed to wear the black hats, all of the troopers wore the light brown/tan fedoras.
Now some presedent day Cavalry units allow their troopers to wear the black hats, but being true -- and real -- Cavalry, the 11th Troopers wear the brown/tan Cavalry hats.
If you see todays 11th Cavalry officers at Ft. Irwin they all wear the brown/tan hats.
So either way is probably ok (In true street racing vocabulary - Ya Run What Ya Brung) -- but it's just the tradition, something the 11th stands by.
The 11th Cavalry store only offers the brown/tan hat.
By the way, I was in 1-How April 67 to April 68 - turret mechanic -- always wondered how the old boys (guns) held up after I left -- maybe have a chat some day.