Okay, before someone downvotes because "it's basically achromia" no. No it is not. It is pretty different.
Leucism results in partial or patchy loss of pigmentation, and has been seen a lot in lions. Most people look at white lions and go "albinism!" Nope. Albinism / Achromia actually does not exist in lions, only leucism. Most images of "albino lions" are really just photoshopped leucistic lions.

Leucism would be a passable mutation, just as it is in real lions. It would result in a small deduction from a lions stats, as its coat would make it easier to spot while hunting or in combat, and would not help it in any way. All leucistic lions would have the same coat and pale blue eyes, along with brown-ish lineart. Leucism would not be achievable via breeding items, and could only occur with at least one instance of inbreeding in it's parents lineages, this would make it closer to reality. Some clean breeders may get pissed at this, but it's just realism. The more inbreeding in a lions pedigree = the higher chance of a leucistic lion being born. After a certain milestone of inbreeding and leucistic lions existing in ones pedigree, males manes will begin to become shorter as the generations pass, despite its parents genetics. And, chances infertility will increase.

I think this would be a cool way to add overlapping mutations. Leucism would be able to overlap with blindness and deafness after a specific amount of inbreeding. This could also serve as a way to prevent too much inbreeding in lions.

For cubs born with Leucism, their chance of survival would ALWAYS be below 99% no matter what.

And this is where I want to introduce a new potential feature! Hesitance to breed. If a lioness is Leucistic, your king may be hesitant to breed with her, thus resulting in a higher amount of breeding chances to result in a pregnant lioness. The following message would appear if your lion is refusing:

"*king* Looks *Lioness' name* up and down, inspecting her off-white pelt and baby blue eyes. He huffs a snarl and turns around despite the smell of heat flooding his nose."

This could also happen with lionesses. If you have a Leucistic king, your lionesses may refuse to breed with him! This is because the lighter a lions mane is, the lower amount of testosterone they have. And your lionesses will notice this!:

"*Lioness* spins around, and aims a swipe at your face, ouch!"
* Neutral - Evil personalities only*

"*lioness backs up, and apologizes, strutting off into the bushes. Rejection sucks, even by your own wives."
* Good - Neutral personalities *

There is no way around this, other than just not having a leucistic king.

Now, time for the actual art! This is just sort of concept art, so it's kinda trashy and rushed.
1.
Good Pose:

2.
Kind Pose:

3.
Neutral Pose:

4.
Default Pose:

5.
Snarky Pose:

6. Evil Pose:

(I still have to do pregnant, jolly, and default male.)
Let me know your thoughts! And please do not click no support without commenting your reason. (Already having achromia is not a valid reason.)