You're not going to like this

The anti-adult colours of orange and green won by default, not because the kids loved the colour. They actually had no strong reactions either way, but in this new kid universe, these colours said to grown-ups, "You're not going to like this and that's alright with us!"

The green of the palette became the viscera. It represents the slime and the goop and all those things you can't do on TV or anywhere else for that matter! Orange became the ruling colour in the actual identity and it was perfect - perfect because it was ownable. In the early 1980s no one was using orange.

Jan Craige Singer on the development of the Nickelodeon logo in the 1980s, from Brenda Laurel's excellent Design Research: Methods and Perspectives (thanks Celia).