The yellow/gold bunnies don't seem to spawn naturally in fields. I have only been able to get them through spawn eggs.
If you use spawn eggs and spam-spawn bunnies, you will get a golden bunny that doesn't spawn naturally.
They should spawn naturally but they don't for some reason.
Environment
Windows PC Minecraft
They do seem to spawn now, if not before. Found one and two babies on the edge of a Forest. I am using 1.8 -Pre1.