Macedonian Phalanx Illustration

[MeinPanzer]

Bythinians were among the last kingdoms to maintain pike troops, up to the time of Julious Ceasar. Chances are that Farnakes household troops would be more uniformed than others-again depending on numbers and material availability.

What's your primary source for this?

Alexander's army acquired rich spoils after Issos-cloth and clothing included. Unless some regulation that we do not know of was enforced chances are that your average pike-man might be wearing a Phoinician(?) or Persian(?) chiton or assorted cloaks from there coutures. The average Greek chiton could also be constructed from cloth with "foreign" patterns.

I don't doubt that some material was appropriated by Alexander's troops, but considering much of the contempt of the common Macedonian for Persian fashion and affectations (Alexander's wearing of Persian robes and the reaction to it), I kind of doubt that it was widespread. The only item of costume that I know was adopted from the Persians was the long-sleeved, double-belted tunic by the cavalry, which persisted until, at the latest, the very early 3rd century BC.

Hellenistic period was a time of endless civil wars. Troops might have been affected by attrition and supply/production limitations.
Poorly armed pikemen in the rear ranks are a valid speculation.

Could be, but we really don't have any idea of who wore what within the phalanx, unfortunately.