In the original novel, the colors of the Life Clock change every seven years: yellow (birth-6), blue (7-13), red (14-20), red and black on Lastday, and black at 21. According to the audio commentary, the movie changed it to 30 because it wasn't realistic to have a cast with all of the characters under 21.
The waterfalls and steps Logan jumps into to get back into the dome are the "active pool" of the Water Gardens in Fort Worth, Texas. At the time, the main pool was nine feet deep. It was closed in 2004 after four people drowned near the spot where Logan and Jessica dove in. When it reopened in 2007, the main pool was two feet deep.
The Love Shop sequence originally ran about four minutes, but required re-editing for the movie to be granted a PG rating. A scene with Box making a nude ice sculpture of Logan and Jessica was also cut. A scene with several characters visiting the Hallucimill shop in Arcade was cut for its depiction of drug use. All of the additional footage and its background music were lost in what is now known as "the great MGM purge", when studio owner Kirk Kerkorian sold off what he could of the studio's extensive archives, and threw out the rest.
The costumes were originally designed to be much more revealing, but that meant spending much more on make-up for exposed skin.