The change in color is a side-effect of being a goo creature, but blue cougars are not a thing of this world, let alone shiny ones. And finding out what he is now probably would NOT be a good idea. Our character (I need to give him a "normal" name still) learns how to do fur, but the color has a more conventional solution...

The bull is the one that turned him this way, and I'll need to name him. He's the "expert" of the two, having been like this quite a while now.

Honestly I just like some sort of limitation on shapeshifting. Though as this isn't exactly "magic" they do have to hold to conservation of mass too,