When the squad applies their camouflage makeup, Littlejohn and Saunders just put a couple lines on their faces, Caje puts on a little more, and Kirby smears it all over his face. Minutes later, the camouflage is different on everyone's faces, and more or less disappears. They all just look like they have dirty faces, as they would on any mission.
The US Army Air Force bombing mission with B-17 Flying Fortresses takes place at night. The USAAF held firm at flying their bombing missions during daylight for precision bombing rather than joining the British Royal Air Force in nighttime area bombing. By the time US troops were on the ground in France (D-Day), USAAF fighter planes had established air superiority over Germany and western Europe. German fighters were no longer a sufficient threat to US daylight bomber raids regardless of German radar coverage, which was the ostensible reason for Saunders' squad to knock out the German radar station while the US bombers bombed at night.
When Saunders and German Lt. Marchand are fighting and Saunders flips Marchand over his back, it's an obvious stunt double for Marchand. His whole face is visible.
When Rawlings starts crossing the stream, his clothes are already damp, probably from a previous take.
When the squad applies their camouflage makeup, they don't bother giving any to Lt. Marchand (impersonating a member of the resistance).