Well... May I quote:
"Melanistic lions may be theoretically possible, but they have never (to date) been reported. Melanism would certainly be a major disadvantage for these animals, who depend on their tawny coat color to blend into their background; a black lion would have serious problems stalking its prey. And it may simply be that lions do not carry the recessive gene for melanism. "
Source:
http://weirdanimalreport.com/article/sadly-black-lions-are-not-real-thing
https://s-media-cache-ak0.pinimg.com/736x/3a/be/34/3abe341f0b64cf9fb34b594dcb683719.jpg
"Melanistic lions may be theoretically possible, but they have never (to date) been reported. Melanism would certainly be a major disadvantage for these animals, who depend on their tawny coat color to blend into their background; a black lion would have serious problems stalking its prey. And it may simply be that lions do not carry the recessive gene for melanism. "
Source:
http://weirdanimalreport.com/article/sadly-black-lions-are-not-real-thing