Leviticus 13:6

And the priest shall inspect him the second seventh day; and, behold, if the plague hath become darker, and hath not gone wider in the skin, the priest shall make him to be clean; it is an obstinate sore, and he shall wash his clothes and be clean.

second a second time

dulled Many scholars have said that this word means “darkened”. Their evidence is the related word found in the phrase, “his eyes were too dim to see” [Genesis 27:1]. They said that the oxymoron “dark white” [:39] is similar to the phrase “white-red” [:19; :43] — i.e., that both pigments appear. But in my opinion, the word here means the opposite of spread , as in “his eyes had ceased to see” [Genesis 27:1]. A related word appears in the phrase “he did not restrain them” [I Samuel 3:13]. The apparent redundancy of if the symptom has not spread is understood to denote the appearance of symptoms elsewhere on the body. Thus there are two indicators: 1) the original symptom has receded; and 2) it has meanwhile not erupted in healthy skin.

the kohen will purify him i.e., he will declare that he is ritually pure, since it was only a mispaḥat . However, if it subsequently spreads, then he will be ritually impure.

AND THE PRIEST SHALL SEE HIM A SECOND TIME THE SEVENTH DAY, AND BEHOLD, IF THE PLAGUE BE ‘KEIHAH’ (DIM), AND THE PLAGUE BE NOT SPREAD IN THE SKIN, THE PRIEST SHALL PRONOUNCE HIM CLEAN. Rashi commented: “Keihah means it has become paler (plague) is masculine, and keihah (pale) is in the feminine, the word keihah cannot be an adjective to nega [meaning: “if the plague is pale”]. Instead, it must mean, as Rashi points out, “if the plague has become pale,” serving as a verb. than its [former] color. [This allows the inference] that if the plague remains in its former color and has not extended in the skin, he is impure.”
This indeed is the sense of the verse. But the interpretation of our Rabbis is not so, for we have been taught in the Mishnah: “To cause to be put in quarantine [for a second week] such a plague which continues unchanged at the end of the first week; to pronounce pure such a plague which continues unchanged by the end of the second week.” And in the Torath Kohanim the Rabbis have expressly said that in the case of garments, if the plague is at a stay at the end of the first week, they are to be put in quarantine [for a second week], and if it be at a stay at the end of the second week, they are to be burnt; but in the case of a person, if the plague be at a stay at the end of the first week the priest is to put him in quarantine for another week, but if at the end of the second week it is still at a stay he is to pronounce him pure. And in Tractate Megillah the Rabbis have further said: “This excludes a leper who has been put in quarantine for a week, whose state of leprosy is determined not by his bodily condition, but merely by days.”). Now if it were necessary that the plague should become dim, then his purity would be dependent upon his bodily condition! Rashi himself explained it there in such language, saying that the leper’s purity is not dependent on the physical state of the plague, for if at the end of seven days a symptom of impurity — white hair or extension of the plague — is not found, the priest is to pronounce him pure although the plague has stayed in its appearance, that is at the end of the second week.. The discussion here relates only to the end of the second week.
Rather, this is what the Sages said: at the end of the second week, whether the plague has paled from the color of snow to [the shade of white of] the lime used in the Sanctuary, or like the white of …

ביום השביעי שנית, “again on the seventh day;” we learn from here that the nega will not become ritually clean unless it had shrunk. This is also how Rashi explains it with the word כהה, i.e. its appearance had become dimmer. If it had become more pronounced or remained static the afflicted person is ritually unclean. The accepted ruling, halachah, however, is that if it did not spread out, the afflicted person is declared ritually clean. This has also been spelled out in the Mishnah in tractate Nega’im chapter 1, Mishnah 3. We quote: ארבעה מראות האלו מצטרפין זה עם זה לפטור ולהחליט ולהסגיר., “Any of these four shades (that have been mentioned before) may combine together to declare clean, or to certify as definite affliction by a nega, or to cause the suspected victim to be shut up.” The first example listed is that the suspected area has remained static at the end of the second week. The expression in the Mishnah להסגר, for shutting up, refers to the first examination after the priest’s visit. The expression לפטור, to declare ritually clean, refers to the visit of the priest after the second week. Similar rules apply if the symptoms had been white like snow after the first week, and by the end of the second week the affected area looked like the whitewashed area of Sanctuary. This is not considered as “having dimmed,” but as having remained static, until the area afflicted has shrunk. Some scholars state that the reason these details have been written in the Torah in this context is to tell us that if the appearance had not dimmed at all, then the afflicted person is declared ritually clean. We are to learn that a change from snow white to whitewashed, or vice versa from snow-white to whitewashed or vice versa, is not to be interpreted as a new type of nega having surfaced. Our author quotes one or two alternate interpretations of the words ביום השביעי שנית, but seeing that the legislation does not apply in our time and we need the prophet Elijah to rule on whose interpretation is correct, this editor sees no point in pursuing this subject at this time.