A common thing you read in WW1 biographies is pilots putting their uniforms over their pajamas and then something such as a sidcot suit over all that lot. This is probably not mere laziness when up for a dawn patrol, but the simple expedient of trapping air in between many layers of clothing to help keep warm. Even on summer days, grass airfields are cold, damp and dewy places early in the morning, as any pilot will confirm. It does not take long for a nice military tunic to end up a disgraceful mess in those circumstances. Even on formal pics of national heroes such as MVR, you can see his tunic often looks a bit scruffy.
Goose fat was occasionally smeared on exposed skin by WW1 pilots, in a manner similar to what you see long distance ocean swimmers doing even today. That and the proximity of oil, grease and petrol accounts for the often filthy and always disheveled appearance of pilot tunics in WW1 pictures, which like things such as the 'Spitfire shoulder' tear on the left side of a pilot's clothing where it catches on the cockpit access lever, became something of a badge of recognition, much like the silk scarf, that being to avoid chafing from clothing when constantly craning your neck about looking for the enemy, but later becoming part of the pilot's rakish look too despite its practical origins.
Strict dress codes in such an environment are largely impractical and would in any case have been largely ignored in the same way that troops in the field make up their own version of what the proper uniform should be for nothing if not practical reasons. A wise commander doesn't even try to enforce dress discipline in a situation such as that, even if he could. It's also worth mentioning that officers had to cough up to have their tunics tailored, which is why many RFC guys stayed in their old Khaki tunics even when there was the new RAF uniform available, since it was likely to end up similarly disheveled if worn on operations. Pilots, and especially fighter pilots have always been somewhat individual and there is no doubt many cultivated a scruffy appearance simply because they could get away with it, with unofficial conventions such as the first button of the tunic being always undone a telling sign of that culture, so it's no surprise to find a wide array of flight suits.
Anyone who has ever been in an open cockpit up over about 8,000 feet will confirm how bloody cold it is, and if you've never done that, then you will almost certainly be familiar with how cold you can get on a speeding motorbike even on sunny days. Add that feeling to the lower ambient temperature when you get up high and you'll have some idea of how cold it can get up there, especially after an hour or so. I've personally found myself freezing my ass off even on summer days in an enclosed cockpit when wearing jeans and a sweatshirt with a (modern) RAF flight suit on top of that gear. It generally starts getting cold once up over about 5,000 feet in Europe, regardless of what season it is. Older aircraft with canvas over a frame fuselage are almost always cold things to sit in when flying about and in winter it is absolutely perishing, although oddly enough, a lot of the time you are so busy you don't notice it, but when you do, it is pretty miserable. You have to really
want to go flying on days like that!
When you see pictures of the brothers Richthofen, you have to bear in mind that they were not short of a few quid, and so they could afford the best flying gear, and in fact being 'celebrities', they most likely got stuff given to them purely for the honour of manufacturers being able to say, 'we made this for MVR'. I'm sure Joe Pilot and all the other mere mortals did not get such things lavished upon them such as the swanky fur suit MVR has on in some pictures, so a greatcoat might well have to suffice. The reverse of that is that people such as
LVR and MVR probably had a wardrobe full of different flying gear.
If you check out the pictures of
Manfred Von Richthofen and Anthony Fokker examining the wreck of of Algernon Bird's Sopwith Pup that was MVR's 61st victory, you can see Fokker is wearing Bird's flying coat and hat, which is indicative of how much some flight gear was prized, as like MVR, there's little doubt Anthony Fokker could have afforded the best that money could buy. It's a fair bet that the boots Bird has on in those pictures got appropriated by someone too before he got packed off to a POW camp.
Al