Commentary for Leviticus 13:4

ועמק אין מראה AND ITS APPEARANCE BE NOT DEEPER [THAN THE SKIN] — I do not know the meaning of this.

ועמוק אין מראה מן העור, even though the sages (Shevuot 6) have said that everything which looks white is described a looking deep, recessed, as the sun appears as if deeper than the shadow, so that the wording of our verse appears to be incompatible with the statement of the sages, seeing that the skin itself is a form of something whitish the Torah means that the relationship of the normal skin to the whiteness of the tzoraat is comparable to the appearance of the shadow to the sun. [a spot of shadow on a bright day, is after all not “black” as is the darkness of the night. In fact, compared to the darkness of the night, it might be viewed as a weak “white.” Ed.]

ועמוק אין מראה, it is not the same kind of white as the other kinds of scales on the skin mentioned thus far.