They actually did wear clothes that were not various shades of grey.
Lol...
October 29, 1989 (from Scientific Progress Goes ‘Boink’, page 23 / The Indispensable Calvin and Hobbes, page 151)
Q. How come old photographs are always black and white? Didn’t they have color film back then?
A. Sure they did. In fact, those old photographs are in color. It’s just that the world was black and white then. The world didn’t turn color until sometime in the 1930s, and it was pretty grainy color for a while, too.
Q. But then why are old paintings in color?! If the world was black and white, wouldn’t artists have painted it that way?
A. Not necessarily. A lot of great artists were insane.
Q. But… But how could they have painted in color anyway? Wouldn’t their paints have been shades of gray back then?
A. Of course, but they turned colors like everything else did in the ’30s.
Q. So why didn’t old black and white photos turn color too?
A. Because they were color pictures of black and white, remember?
On that note, go see They Shall Not Grow Old. WWI was not fought in black and white. Stay thru the credits for the Peter Jackson interview at the end.