Back then, movies were black and white because they had cameras that could only see black and white. In the late 1900's and early 2000's, they developed color cameras. But the common resolution and screen size was 640x480 or 4:3. Nowadays, in the late 2000's and early 2010, the widescreen format was more commonly used for many reasons. Today, the common colors are RGB 1M colors, and the resolution is 16:9. Some movies like to go even farther, like me, and use 21:9,which is super widescreen. That is more immersive than 16:9, and gives the watcher a wider, better experience.
