Thunder is a chocolate smoke color.
This is a rare color in any breed. 

The silver gene is expressed as solid white hair at the root. Then each hair shaft is tipped in chocolate which makes the white undercoat appear smokey.
It is a yummy color!

At the moment, he is still growing his coat, so the smokey coat is more obviously seen.
The face is darker since the hair on the face is always a shorter coat.

It is a dramatic look and his curls are soft and luxurious!