The first reason is this thing called color theory — which uses a color wheel to show which colors complement each other.
Well on TV, they use a ~cool~ color wheel, called the RGB model. In this model, YELLOW actually complements BLUE.
And blue is one of the most common backgrounds in animation:
The second reason is color psychology, which examines what colors are associated with. For instance, colors like red are associated with negative stuff, like rage.
But yellow is an ACTIVE color, and it's associated with happiness and energy. So obviously you want a character that reflects those qualities.
The third reason is our eyes. They pick up yellow pretty quickly. Here's a science thing to show that:
This is why stuff like caution signs and taxis are yellow. They stand out.
And SO DO YELLOW CHARACTERS.
Another bonus reason: Most people who are colorblind can still see yellow!
In conclusion, yellow characters go well with the commonly used blue background, are associated with happiness and energy, draw attention, and can be seen by people who are colorblind!
