Why are so many iconic animated characters yellow? The answer lies in random personal choices, scientific and marketing theory, as well as the colour of the sky.
Minions are yellow because the animators thought their shape resembled Kinder eggs. Winnie the Pooh was based on a World War 1 veterans real pet bear and author A.A. Milne based Pooh's look on his son's yellow teddy bear. But The Simpsons are the best example of yellow characters being used in animation for practical reasons. When The Simpsons first premiered, its creators wanted the show to be instantly recognisable when viewers were quickly flipping through the channels. Rather than having a peach skin tone that was used most often in animated series at the time, The Simpsons were bright yellow and really stood out to the average channel surfer.
But why yellow and not another colour? ChannelFrederator has attempted to find out in the video below. There's no single answer to that question. Instead, there's a combination of factors that are rooted in colour theory and colour psychology. For instance, the colour wheel that's used for television is the light-based RGB scale. Unlike the standard RYB colour model, yellow is complementary to blue. And if you want your characters to stand out against a background, blue is a great choice because it will always be the background for scenes set outside on a sunny day or in SpongeBob's case, under the sea.
From a psychological perspective, a definitive scientific reasoning is slippery. But among other things, yellow is often associated with being active, warm and energetic, as most cartoon protagonists tend to be. But also, looping back around to The Simpsons desire to stand out, yellow is for many reasons the most visible colour in human perception.
Check out the video in full below. It contains more detail about the reasons for yellow characters in animation and it has a lot of interesting factoids about how colour choices have affected animation in general.