What does “the colour slowly changes from 14 to 23” mean?

It’s a lyric in the title song from the 1968 film Skidoo, in which Carol Channing extols the virtues of free thinking and embracing the grey areas of life.

My guess was that it had something to do with colour TV (given the era) or LSD (given the content of the film), and there’s always that expression “23 Skidoo”, but I’m not sure.

Music and lyrics by Harry Nilsson, and it’s on Spotify and Youtube if you want to listen for yourself (but it’s Skidoo/Goodnight Mr Banks, not Skidoo/Commercials).