Someone uploaded a tastefully/abominably (take your pick) colorized version of the existentialist science fiction classic, The Incredible Shrinking Man, which you can watch for free on The Internet Archive, or right here at the bottom of this post.
The movie is based on the novel, The Shrinking Man (1956), by Richard Matheson, who also wrote I Am Legend, and a lot of Twilight Zone episodes. The protagonist, Scott Carey, finds himself in a terrifying situation as he gradually shrinks due to exposure to a radioactive cloud. Yet this physical transformation symbolizes far more profound changes. As Carey shrinks, he is effectively disappearing from societal norms and undergoing a profound alienation from his previously familiar world.
I also recommend the Criterion Collection edition, which includes a lot of great bonus material including a program on the groundbreaking special effects and an interview with the director, Jack Arnold.