Colorization and hand coloring* are names for the process of coloring film and pictures by hand and by frame. There are oils, watercolors and dyes used for this techniques applied to black and white film and photos.
This entry is to honor the work of early Hollywood to attempt to make color movies and pictures happen.
This picture has been colorized--it is from Ingrid's very first part in a film as "girl in line."
This is a colorized photo from the 1944 black and white film, Gaslight.
Colorized photo of Cary Grant and Ingrid Bergman from Notorious. I wonder if Robert Capa took this photo?! Wouldn't that be sexy?
There was a movement in the 1980s to colorize films that were originially done in B&W...I'm not a fan, but I thought in the 1920s and 30s it was a perfectly legit way to try and improve film. They also tried to do this to It's a Wonderful Life, I didn't like that colorized either. Lol.
*wikipedia information is subject to change and is not a reliable source. I just used it to emphasize my point, I'd suggest further reading if you're really interested in the history of colorization (also--different forms of colorization have happened throughout the history of film and photographs, so it's completely more complex than the wiki-answer).