Black and white film has undergone a lot of changes over the years. One of the bigger changes was making it less blind to certain colors.
Yes, less blind. If you look around you, different colored objects will appear to you at different brightnesses, and you might be able to imagine how the scene looks in black and white, simply by translating the brightnesses into grey levels.
And that's how many black and white films work these days. They try to create a black and white picture that reflects the perceived brightness levels that you see with your eyes.
But originally, black and white film would translate colors very differently.
Look at the visual spectrum. It starts right beyond infrared, goes through red, orange, yellow, green, blue to violet and then disappears into ultraviolet. Infrared and ultraviolet are black to our eyes, simply because we don't have the right receptors to see these colors.
Now imagine a black and white film that can see an even narrower range, film that can only see part of the colors. And that's exactly what black and white film did in the old days. It was blind on the red side of the spectrum, so whenever it saw red light, it would register that as black. We call that an orthochromatic film. Only some time after the 1950s did black and white film become more sensitive to other colors. A film that sees the entire visible spectrum is called a panchromatic film.
Here's a snap I took of the same scene, but this time with a digital camera:
Compare the two and you will notice that the black and white film is very sensitive on the blue side, but it almost doesn't have any sensitivity on the red side of the spectrum. Blue renders almost identical to yellow, and green is somewhere in the middle grey area. In the early days of black and white photography photographers had to learn how to see in black and white to get to the picture they envisioned, and still today a lot of films have their characteristic look that's at least partially based on how the different wavelengths are rendered on a scale from black to white.
Back in the day, art went so far that during early black and white film productions, the actors had to wear bright and colorful make-up so that a normal looking black and white image could be achieved. Imagine an actor with green lipstick to avoid the lips from going all black on the film. These early film sets must have looked very colorful.