Macedonian Phalanx Illustration

[MeinPanzer]

Well, untill a learned of Philips helmet I did not no of a single Greek iron helmet. But that helmets were painted is accepted wisdom AFAIK.

To be fair, these could simply be "tinned" bronze helmets as well- they need not necessarily be made of iron, just look like iron, or "silvered."

I know my idea is goes against accepted notions. I just looked at the cuirasses on the Sarcophagus and comared them with Alexander's armour on the mosaic and I thought: What if the light purple represents iron and the light yellow linen. Then these two armours would be nearly identical. The sarcophagus even has the same red edging as the painting.

The Alexander sarcophagus had extensive painted detail on it that was still very well preserved when discovered- right down to images of Persian kings with neatly-patterned clothing painted on the insides of Persian shields. If they were supposed to be scale, they would have painted scale on. So on top of not being the usual colour to represent metal, they also haven't actually painted any scales on there when you would expect them to do so.

I think you are trying too had to draw parallels between the Alexander sarcophagus and mosaic. Almost all similarities between the two are due to the general styles of Hellenistic art. Everything about the Macedonian figures (and the Persian figures, for that matter) - Alexander's equipment and costume, the type of helmets worn, the colours - differ, so straining to draw any parallels doesn't bear much fruit, unfortunately.