CALVIN: Dad, how come old photographs are always black and white? Didn't they have color film back then?
CALVIN'S DAD: Sure they did. In fact, those old photographs are in color. It's just the world was black and white then.
CALVIN'S DAD: Yep. The world didn't turn color until sometime in the 1930s, and it was pretty grainy color for a while, too.
CALVIN: That's really weird.
CALVIN'S DAD: Well, truth is stranger than fiction.
CALVIN: But then why are old paintings in color?! If the world was black and white, wouldn't artists have painted it that way?
CALVIN'S DAD: Not necessarily, a lot of great artists were insane.
CALVIN: But ... but how could they have painted in color anyway? Wouldn't their paints have been shades of gray back then?
CALVIN'S DAD: Of course, but they turned colors like everything else in the '30s.
CALVIN: So why didn't old black and white photos turn color too?
CALVIN'S DAD: Because they were color pictures of black and white, remember?
(CUT TO: EXT. Tree limb, Calvin talking with Hobbes)
CALVIN: The world is a complicated place, Hobbes.
HOBBES: Whenever it seems that way, I take a nap in a tree and wait for dinner.