S. R. Faruqi:

There's an affinity between the whole entire heart becoming 'pain', and the 'disease' of passion. In 'we have the disease/sickness of passion' there's also an implication that this disease has arisen of its own accord. For example, they say fulāñ ko diqq kī bīmārī hai [=a fever]. Consider also that the expression bīmārī hai is not used for ordinary everyday little illnesses; for example, they don't say fulāñ ko zukām kī bīmārī hai or fulāñ ko bad-haẓmī kī bīmārī hai [=a cold, or indigestion].

The expression bīmārī hai is used for some severe disease, or again for some chronic disease, or again to express something in simple language. For example: (1) fulāñ ko chhīñk āne kī bīmārī hai [=sneezing]. (2) fulāñ ko peṭ kī bīmārī hai [=stomach trouble]. (3) fulāñ ko gaṭhiyā kī bīmārī hai [=rheumatism]. If instead of bīmārī they had said marẓ , then this effect would not have been attained.

By mayyit ke rangoñ is meant 'like a corpse', but it also has an affinity with a yellow/pallid color. Through the use of the word mayyit the implication has also been achieved that the culmination of this disease is death. It's a great verse of 'mood' [kaifiyat]. In the tone there's a style like that of some hopelessly sick person, but the mention of the 'disease of passion' is not without dignity.

The image of the corpse-like color he has used in the first divan as well, but the same effect has not come into it [{259,10}]:

dikhāʾī deñge ham mayyit ke rangoñ
agar rah jāʾeñge jīte saḥar tak

[we will appear like a corpse,
if we remain living till the dawn]

In the fifth divan there's a mention of the corpse-like color, but the first line, in which this image appears, has remained extremely loose. Although indeed, the second line is excellent [{1553,2}]:

jīte-jī mayyit ke rangoñ log mujhe ab pāte haiñ
josh-e bahār-e ʿishq meñ yaʿnī sar tā pā maiñ zard huʾā

[while I'm alive, people now find me with a corpse-like color,
in the tumult of the springtime of passion, that is, from head to foot I became pale/wan/'yellow']

[See also {1494,3}.]

FWP:

SETS == WORDPLAY
MOTIFS == LIFE/DEATH
NAMES
TERMS == AFFINITY; MOOD

Here's Ghalib's take on the lover's color becoming zard :

G{7,2}.

For them both, as so often, it's chiefly wordplay that energizes the verse. Ghalib's rang uṛnā and Mir's mayyit ke rangoñ feel like the starting points, the seeds, from which the verses grew. Yet we feel that their 'styles' are so different-- but do we really have the vocabulary with which to capture and analyze this difference? People throw around words like 'style', but it proves very difficult to make systematic, thoughtful use of them. It's like 'time'-- we all know what it is, until we actually undertake to describe it.