S. R. Faruqi:

If rahte the is assumed to be a Dakani style of speech, then this will be an expression of vain longing; that is, 'If only buffeting had remained in the eyes!'. In this situation, the meaning becomes that if from time to time the eyes (which are rivers of blood) had overflowed and flooded, then a scene of a hundred colors/styles would have been visible. Mir has used the past habitual to express longing in a number of places, in the style of 'old Urdu'. From the sixth divan [{1898,7}]:

aage bichhaa ke na:t((a vuh laate the te;G-o-:tasht
karte the ya((nii ;xuun to ik imtiyaaz se

[having spread out the leather-piece, she 'used to bring' sword and basin,
that is, if she 'used to commit' murder, then with a single/particular/unique/excellent discrimination]

Now this river has gathered itself together and gone back to its proper level; for this reason, in every direction there's nothing but colorlessness upon colorlessness.

If rahte the would be taken as the past habitual, then the interpretation changes a bit. Without you, in the eyes there was constantly a show of a hundred colors/styles; but now the eyes have become dry, so this state of affairs no longer remains. If only this river of blood in the eyes would sometimes rise up and overflow, then this same scene would be visible again.

There are a number of points in the verse. The phrase 'without you' apparently seems unnecessary, because obviously at that time too there's the 'mood' of separation. Only from the hundred-colored buffeting of the eyes and the mention of the river of blood does it become clear that it's the season of separation. If it's looked at in this way, then even without 'without you' the verse seems to be complete. But there's also the possibility that this might be a verse not of separation, but of union.

That is, during the time of union the sight of the beloved is vouchsafed, but the pain-loving heart has also remembered the days when the eyes were a river of blood, and for this reason the whole world seemed colorful. These are the days of union, but he still hasn't forgotten the relishes of separation. When she was not there, then there was a hundred-colored scene in the eyes, because the eyes were red with blood. If sometime that river of blood again overflowed, then that interesting scene would again be visible.

Between this reading and the other reading (that is, if rahte the would be taken as contrafactual), then the pleasure is that the second line remains a bit incomplete, but the thought becomes complete. That is, after the line some such utterance as this is implied: 'then how fine it would be' or 'then the same pleasure would remain', etc.

The third point is that in the second line the word 'this', which applies to the eyes being settled/established, is very fine. The use of such a pronoun, in which there would also be an element of emphasis/stress, is perfect eloquence [balaa;Gat].

FWP:

SETS == GROTESQUERIE
MOTIFS == EYES
NAMES
TERMS

The image of the eye as suddenly overflowing, so that a river of blood gushes out from it, is really not very appealing.

Note for grammar fans: In this case the 'always' construction, cha;Rhaa karnaa , 'to always rise up', seems contradictory to 'from time to time' [kabhuu kabhuu]. But perhaps the effect is meant to emphasize the insistent strength of the rising up, or to reflect the confusion in the speaker's heart and mind.