Color of British Commando Beret?

I’m not sure, but my impression is that the British WWII paratrooper beret was red: Sean Connery wore a red one in A Bridge Too Far, in which he played a British para.  I think the SAS beret was tan in WWII, but I can’t vouch for that.  There’s a photo on Wikipedia (in the article on the British Commandos) captioned “Commandos wearing the green beret and carrying the Bergen rucksack during the Normandy landings” – but the photo is black and white, so the accuracy of the caption isn’t clear.

Try the Osprey book “British Commandos 1940–46”,  ISBN: 9781841769868.  Or Google “osprey british commandos” and go to the “Images for osprey british commandos” part of the results.

Paratroop regiments in the strict sense are units that specialize in parachute jumps.  The Royal Marines (“we can do everything the Army can do and we can do everything the Navy can do,” as one of them told British author H.V. Morton back in the 1930s) aren’t paratroopers as such, though it’s probable that some of them are jump qualified.  The SAS are a special forces outfit of the British Army, not a para unit, but they’ve always been very versatile in their methodology so it’s likely that parachute insertion is a technique in which at least some of them train.  Their Royal Navy counterpart is the SBS, the Special Boat Service.

I think officially only the Royal Marines are commandos but many people call special forces units commandos even if that is not their official title.

“Commandos”, strictly speaking, refers to the forces that were set up and run by Combined Operations Headquarters, commanded by Louis Mountbatten.  They were (I believe) an inter-service group, and they were specifically set up to conduct raids on Occupied Europe.  They weren’t the same as the British Paras or the SAS or the Royal Marines, which were all specialized units within either the British Army or the British Navy.  The main connection between the Commandos, the Paras, the SAS and (over on the American side) the 82nd and 101st Airborne and the Army Rangers is that all of them were elite units of one sort or another: highly trained, able (and often expected) to function in small groups or on their own behind enemy lines, and often skilled in close-combat techniques.  The Royal Marines don’t necessarily fit that pattern, in the sense that their primary mission wasn’t to conduct raids or to conduct parachute drops or to take specialized objectives like Pointe du Hoc (which was a Ranger target on D-Day).

To give a US parallel, the USMC created two raider-type batallions during WWII which were much more Commando-like in training and function than the Marines in general.  The USMC was (and is) highly skilled in conducting amphibious landings against very tough targets, but if you compare Iwo Jima against the raid on Makin Island by Carlson’s Raiders (the 2nd Marine Raider Battalion), you’ll see that Iwo Jima was a large scale take-and-hold invasion while Makin was a small-scale hit-and-run raid.

But it’s true that elite forces in general have a disproportionate affectation for berets.  It’s a romantic soft spot among these otherwise very tough guys.