My hoplites do not share a color scheme on their uniforms and each one has a different design on his shield. I've been told that a unit looks better when all the fighters are uniform, but I have declined to follow that advice. For starters, I collected these hoplites from half a dozen different manufacturers and since their sculpts don't really match (some have a breastplate and others a linothorax; some have a tunic and some are naked), matching the outfits is out of the question. There's also the issue of my getting bored painting the same design over and over.
But the larger issue is a historical one. A hoplite was a middle class man rich enough to afford panoply but not a horse. Except in Sparta, where the state issued each soldier a red cloak (doesn't show blood) and a Lambda shield, a citizen was expected to provide his own armor. In many cases it would be handed down from father to son. I doubt your average phalanx was uniformed.
The Greeks were a far more individualistic culture than the more collectivist cultures of their contemporaries in Persia, Egypt, and the rest of the Near East. Each hoplite's shield was his opportunity to make a statement -- about his self-image, artistic sensibility, even his sense of humor. One fighter had nothing but a life-sized fly painted on his hoplon. He explained that in battle, he would get right in the enemy's face and the fly would seem to be the size of an elephant or a dragon or something. Anyway, every hoplite gets a unique shield. Here are my better ones.
An octopus, a trireme, and a woman coming her hair. I love putting womens' faces on hoplons.
Bull, swan. These are two of my best one-color designs, just using the background color as negative space. Sometimes the simplicity of one color designs makes them look a little kindergartenish, but sometimes I get elegant simplicity and I think that's what I've gotten here.