Cats and dogs are expected to give birth to babies that share similar physical traits to their parents such as the color and pattern of their fur. But imagine the surprise of a North Carolina family when their white German Shepherd gave birth to a puppy with a fur color so different from its mother.

In fact, it can be said that the puppy’s color is unnatural even by dog standards. Instead of coming out white like its mommy, the puppy is shockingly lime green in color, according to Daily Mail.

The Stamey family from Canton was excited when the white German Shepherd, Gypsy, started giving birth on January 10. Everything went smoothly until the fourth one came out – its lime green fur in sharp contrast to its more conventionally colored siblings.

Gypsy gave birth to a total of eight pups. But  only the fourth one is lime green in color. The rest are either black or white in color.

“Then I realized the puppy was moving, and he was lime green,” Shana Stamey told WLOS. The family posted some photos of the newborn pups where the lime green one stood out against his black and white siblings.

“Hulk!” Shana Stamey replied when asked what the pups name was. “It was lime green. He was super mad. So, yeah, he became Hulk. We thought about Gremlin, yeah, Pistachio. We call him Mr. Green sometimes.”

Turns out that there’s a scientific explanation on why Hulk, the puppy, might have ended up with a green fur.  

According to Suzanne Cianciulli, a veterinarian technician at Junaluska Animal Hospital, Hulk got his surprising color from his mother's sack. Meconium, an infant mammal's earliest stool, might have dyed the puppy while still inside his mother’s womb.

“The sack that they're in when they're in their mom, there can be meconium in there and that tends to stain them,” Junaluska Animal Hospital veterinarian technician Suzanne Cianciulli explained.

Another potential cause for the color is Biliverdin. It is a green bile pigment that can be found in a dog’s placenta.

The lime green color of Hulk’s fur is likely to go away in a couple of weeks. “Mom licks it away until I bathe it and then, I guess after a couple of weeks, it will finally like fade out,” Stamey said.