In the movie Spaceballs, when Spaceball One goes to ludicrous speed, there’s a joke that says, “They’ve gone to plaid!” Ever since I’ve seen this movie, I haven’t been able to get this joke. What is this supposed to mean?
You are trying to understand this joke at too deep a level. The joke is saying that a ship and its contents traveling at “ludicrous” speeds would undergo some fundamental change. It is a kind of exaggeration of the laws of physics that state that as an object’s speed approaches the speed of light, it’s mass will increase. The writers just took this idea and twisted it. Plaid is a funny color scheme (more so than most other color schemes) so that used it as the change that happens when you travel at high speeds.
Airplane 2 used a very similar joke when the moon shuttle blasted to hyperspeed. All of the passenger’s faces turned into a mask of a game show host.
Both of these movies have many silly lines like this. Sometimes the writer went with what would strike people as funny rather than what would hold up to careful dissection.