Farraday's (Van Johnson) shirt color changes during his street brawl from a pale olive to a near brilliant emerald green. Its material composition also changes from a flat to a satin-like sheen.
Faraday grabs the barrel of the Gatling gun with his hands. The barrels would be so hot from firing that it would have burned his hands.
The clothing of the characters is rarely period correct. Men wear full front button shirts which were not invented (nor popularized) until the 1920s. belt loops are on pants are seen and they were not used until the early 20th century. A woman is shown riding on a wagon without a bonnet to cover her face from the sun, nor her hair from the trail dust. And many of the hats worn are clearly made of materials (felt for example) that was not used during the time period in which the film was set.
Many of the firearms shown are not those that would be used (or even invented) during the Civil War. Winchester are shown and they wouldn't be invented until after the Civil War and would not be widely sold until the early 1870s.
Most of the men in the film are clean shaven. Not only was this not period correct (most men had at least a mustache if not full facial hair) being clean shaven was difficult and potentially dangerous (the possibility of infection is high) in areas where clean water was scarce.
Joanna Dru is clearly wearing foundation and eyeliner. Neither of these were invented until the early 20th century and a woman in a rural area wouldn't have worn them, especially since they would have attracted dust to her face and eyes.