1

A lung that's found to have (even) any amount of something black as ink or it (resembles) the appearance of flesh or it's yellow, amarillo (Spanish) (and in German, gel), whether it looks like egg yolk or crocus or hops, it's treif. Likewise if it looks like a wood chip, that it's pale as a wood chip, it's forbidden. An opinion says that's if it looks like palm branches.

Rema: And some say even if it's white like egg white it's treif (MHRY"V) (ערוך ערך כחל ורוקח וע"פ) and that's the practice.

2

Any of these Mar'ot (appearances) do not invalidate it until it's inflated and he rubs it by hand, and if it changes to a permitted appearance it's permitted, but if it retains its appearance it's forbidden (all the poskim excluding R"Y in Tos.)

3

There is an opinion that these Mar'ot do not invalidate unless the change is in the skin because of it, and not because of Mugla (pus) inside it.

Rema: Similarly if the altered appearance is due to black hair or blood clot in the lung it's kosher (found written in the name of R"Y Mulin).

4

If it's not black like ink but instead appears blue (in Yiddish/German, blau and the shade of the sky) (MHRY"V) or greenish like leek or it looks like the liver (or the shade of the spleen) (B"Y and BD"Y in the name of MHRA"K) or it's red, even if the most extreme red, it's kosher.

Rema: And some say if there's a wound on the wall against the lung then red is treif and it needs to be checked after this (Tur, R' Yerucham, and Rosh in the name of HR"M, and it's the opinion of Rabbeinu Efraim and B"Y in the name of BH"A. The other poskim did not dispute it, but their words imply the opposite, and a few dispute it openly, see there); and that's the custom.

Even if the whole [lung] is that color. Also if it has multiple colors of these kosher appearances - it's kosher.

5

If (the lung) has Klipot (husks, peels) like a Netek (scab, skin eruption, scall (of Tzaraat in Lev. 13:30)) but it's intact, it's kosher.