When Doraemon lived in the future, he was yellow and had ears. But, one day, a mouse robot ate his ears and Doraemon cried so hard that the tears rubbed the yellow off. That's how he turned blue. ... He was a defective robot who was auctioned off and sold to a very poor family.

What is the original color of Doraemon?

In "The Doraemons" story arc (and the 2112: The Birth of Doraemon short film), it is revealed that Doraemon's original paint color was yellow.

Why Doraemon is afraid of mouse?

One day when Sewashi was making a small clay figure of Doraemon, he ordered a robot mouse to eat the ears of the Doraemon sculpture, to make them look more like the ones in a 3-D rendition of Doraemon. But the mouse ended up eating the ears of the real Doraemon, which caused him to fear mice.