Aspect warriors should be, imo, the colour of their aspect shrine not their craftworld. But having said that there are a fair few different shrines so each aspect warrior shrine will look different while still holding true to the basic design of that aspect. For customisation you could have loin cloths, spirit stones and other area's (such as the dire avengers crest on their helms) be able to have their colour changed and maybe a trophy or 2 (and these could have been received from another eldar from a different aspect). But I don't think massive customisation really fits with what aspect warriors are
No, Aspect Warrior can be uniquely colored depending on the heraldry of their Shrine, but the amount of cusotmization varies. Looking at my Eldar Codex, Dark Reapers can change the color of their firearm and topknot, while Fire Dragons can customize the color of their faceplate and second layer of armor/bodysuit. Exarchs all seem to have the ability to customize their armor as which. Honestly, there doesn't appear to be clarification for it in the Codex, Aspect Shrines may have their own completely unique colors, and can color their troops (uniformly) whatever they wish.
In regards to the whole helmet removal thing, it will be an option, the question is how it will be handled for Eldar. By having 3 more primary classes than other factions, the team has already proven that they are willing to make significant changes to keep the Eldar unique and true to lore.
I've always dug Saim Hann Dire Avengers Not so much their Biel-Tan equivalent. I love me some Sword Wind, but euch.
But what I was saying is that Aspect Shrines seem to have their own colors that may reflect their craftworld, but are individual. The Fire Dragon I posted has to be shrine colored, not Craftworld, as to my knowledge there is no Craftworld with Blue, Yellow, and Black as their colors. Fire Dragons normally wear and orange bodyglove that matches their armor, but the example posts has a black one. Which is fairly unusual for Fire Dragons and doesn't match any known Craftworld.