Why did the Pikachu cross the street

There was a pedestrian crossing, and the pedestrian light turned green. The cars in the intersection properly gave the right of way to the pedestrians, which included one Pikachu. The pedestrians then crossed via the striped lines painted on the floor to get to the other side. However, a question that must be asked is how a rodent can naturally grow yellow fur and a lightning shaped tail

To get away from the Thunder Stone.

Ryechu

But why is Pikachu yellow?