Biblical Leprosy was defined as white in the skin:

Leviticus 13:3

“And the priest shall look on the plague in the skin of the flesh: and when the hair in the plague is turned white, and the plague in sight be deeper than the skin of his flesh, it is a plague of leprosy: and the priest shall look on him, and pronounce him unclean.”

Leviticus 13:9-15

9 When the plague of leprosy is in a man, then he shall be brought unto the priest;

10 And the priest shall see him: and, behold, if the rising be white in the skin, and it have turned the hair white, and there be quick raw flesh in the rising;

11 It is an old leprosy in the skin of his flesh, and the priest shall pronounce him unclean, and shall not shut him up: for he is unclean.

12 And if a leprosy break out abroad in the skin, and the leprosy cover all the skin of him that hath the plague from his head even to his foot, wheresoever the priest looketh;

13 Then the priest shall consider: and, behold, if the leprosy have covered all his flesh, he shall pronounce him clean that hath the plague: it is all turned white: he is clean.

14 But when raw flesh appeareth in him, he shall be unclean.

15 And the priest shall see the raw flesh, and pronounce him to be unclean: for the raw flesh is unclean: it is a leprosy.

Leviticus 13:18-20

18 The flesh also, in which, even in the skin thereof, was a boil, and is healed,

19 And in the place of the boil there be a white rising, or a bright spot, white, and somewhat reddish, and it be shewed to the priest;

20 And if, when the priest seeth it, behold, it be in sight lower than the skin, and the hair thereof be turned white; the priest shall pronounce him unclean: it is a plague of leprosy broken out of the boil.

Leviticus 13:24-25

24 Or if there be any flesh, in the skin whereof there is a hot burning, and the quick flesh that burneth have a white bright spot, somewhat reddish, or white;

25 Then the priest shall look upon it: and, behold, if the hair in the bright spot be turned white, and it be in sight deeper than the skin; it is a leprosy broken out of the burning: wherefore the priest shall pronounce him unclean: it is the plague of leprosy.

Leviticus 13:42

“And if there be in the bald head, or bald forehead, a white reddish sore; it is a leprosy sprung up in his bald head, or his bald forehead.”

Miriam became leprous and her skin turned white (meaning her skin was not already white)

Numbers 12:10

“And the cloud departed from off the tabernacle; and, behold, Miriam became leprous, white as snow: and Aaron looked upon Miriam, and, behold, she was leprous.”

Moses’ hand became leprous, turning white (meaning his skin was not already white)

Exodus 4:6

“And the LORD said furthermore unto him, Put now thine hand into thy bosom. And he put his hand into his bosom: and when he took it out, behold, his hand was leprous as snow.”