ETA: I forgot I had the book with me, so I rewrote this.
Listening to the audiobook version read by Martin Freeman, I came across an art history reference.
In chapter 16, Arther Dent travels to the Cathedral of Hate. According to the audiobook (and book), “The unspeakable details that these colors picked out were gargoyles that would have put Francis Bacon off his lunch.”
Source: Douglas Adams, “Life, the Universe, and Everything,” from The Ultimate Hitchhiker’s Guide to the Galaxy, New York: Random House, 1982, 397.