I was playing Pokemon Stadium with my Electabuzz when I saw that the opponent also had one, and it wore this sickly yellowish-green color:
My Clefairy, A.K.A. Fantasy, managed to defeat him easily. I think it looked like this because I had an Electabuzz of my own, called Zapper (Get it? He loves the TV, and electricity.) and to keep them apart the other one was forced into changing its fur color.
I wonder what the science is behind that instant fur coloring change, but maybe it’s just as easy as this:
I mean, they always say that in science, the easiest solution is the most probable answer.
First image from: Taken by MartianOddity
Second image from: http://i734.photobucket.com/albums/ww350/KyosukeKiryu/Pokemon/pokemon2.png
Third image from: http://blurppy.files.wordpress.com/2012/10/spray-can1.jpg