So, while this might come off as fantasy-racist, I can totally see the Imperium saying "all ________ look the same to me, and look even better dead!", so I'll risk it. Even various pieces of art, some fan-based, some "official", significantly differ in what Eldar look like. Some look like gorgeous, Human women, or lithe, statuesque men, with slightly odd features, angular faces, pointy ears, etc (ex. RT core, p357). Others look pretty much like Tolkien Elves in SPEHSS, with a different skin tone, significantly different, less human features, maybe even more exaggerated ears, but still more like a Human in movie make-up (maybe most fan-art), and then you get weirder stuff, like almost chalky white skin, large dark eyes, with little, or no whites, maybe cat's eye pupils, spots, and on (ex. RT core, 334). So, as much as I love the Eldar, I'm not even entirely sure ehat they actually look like, some of the time, and maybe they are all correct, as, as a species, Humans can pull a certain, vast range of diversity, too.

Now, this BS DOES have a point. So, earlier, I asked about characters dying in the Expanse, as I needed a way to get one Rogue Trader out of the way, but not messily, in order to make room for the current one to fill the spot, and the answer I came up with is DE poison. To keep it short, a Calixis world known for donating massive tithes of troops had just done so, to feed the unknown conflict in Jericho, but they actually over-taxed their resources, and were now vulnerable. The Dark Eldar, being pricks, and fond of good, gladiator stock, pounced, and the Navy assets weren't able to respond. Antoss Qel-Drake did, though, and engaged the Dark Eldar, in orbit (here's hoping they use ships, and everything isn't Webway raids, and that they are at least remotely similar to other Eldar craft). Things went better than expected, and they boarded, but the DE put up a hell of a fight, and a Lhamaean scored a hit on Antoss with a dart. Unknown to them, it was a strange toxin, keyed to be neutralized by adrenaline. Getting injured, his crew pulled him out, pissed as hell. They destroyed the DE ship, but the terms were shoddy, and Antoss stayed furious for a few days. It wasn't until he calmed down, enroute to Scintilla, that the poison did its work, and he had one of those heart attacks that actually destroys the heart muscles; there was nothing his crew could do. His death opened the way for Aedan, whom you've all had to hear about, to take the mantle of Rogue Trader.

------tl;dr THE POINT IS BELOW-------

Well, here's my actual quandary: how similar are the Eldar, and the Dark Eldar, two facets of a once united race, actually look? If you eliminate the fact that a Dark Eldar often dresses in clothing made of razor blades, spiky bits, and braided garrote wire, do they look much different than their Craftworld kin? I would've thought yes, due to living in the Webway, with no sun, and other stuff, but the CW Eldar live on starships, and Humans that do that, over generation, the Void Born, certainly stand out, so they both tend to live out of the light, and blah. Aedan has had several dealing with the Eldar, in the form of Corsairs, some good, some bad, and then there's some story bits, after that. He knows, though, that his dad was aced by the Dark Eldar. Would he be able to tell the difference? If a DE wanted to masquerade as one of their CW cousins, could they? Again, the art is not compelling, but it's fan art, for the most part, and the Dar Eldar are conniving, clever, and sneaky, when they care.

Compared to a CW Eldar, what does a Dark Eldar look like, and how observant would you have to be, before saying "you all look the same to me!" )? Just curious, thanks much.

Have you looked through the images in the Soul Reaver and the Dark Kin books? Some of them don't look anything like Eldar and some look like they could pass for Eldar if they tried.

I'm not sure if there's any system which has playable Eldar and Dark Eldar but it might be worth comparing what they get as characteristics as that often reflects physical appearance.

RT only has Dark Eldar as playable character, no other system has other species. Unless you count Abhumans from OW.

If they have soulstones, they are craftworld, if they don't, then they are probably Deldar. (of course the trick is knowing what a soulstone looks like)

Now Harlequins could be both if I'm correct, but they stand apart of the other Eldar groups.

Unless they're eldar that live on Maiden Worlds (or whatever they're called) or Rangers (the wandering nomad ones).

What do you mean by "unless they're Exodites or Rangers?"
Both of those groups have soulstones, the Exodites from their World Spirits (aka planetary Infinity Circuits) and Rangers because they are still Craftworld Eldar and don't want their soul getting nommed when they die.

Unless they're eldar that live on Maiden Worlds (or whatever they're called) or Rangers (the wandering nomad ones).

Exodites. But i think they also use soulstones, rangers definatly. And Exodite souls would meld with some planetary version of the infinity cirquit so that might require a soulstone. (Basically the ones without 'stones are the ones hyding in the webway)

To answer Venkelos question; The DE could masquerade as their craftworld kin, but they don't (or maybe once) because:

A: They hate their cousins and don't wanna dress up like them.

B: Nobody can tell the difference anyway.

C: And if they did they wouldn't care: Orks don't care, Necrons don't care, Slaanesh doesn't care, tyranids definatly don't care.

Even the imperium doesn't care, after all "suffer not the xenos to live" unless the xenos help you fight chaos/nids, in wich case it doesn't matter what type of eldar they are and it's ok to kill them after the battle.

What do you mean by "unless they're Exodites or Rangers?"

Both of those groups have soulstones, the Exodites from their World Spirits (aka planetary Infinity Circuits) and Rangers because they are still Craftworld Eldar and don't want their soul getting nommed when they die.

When I see reference to "craftworld" eldar it just brings to mind the ships. But not all eldar live on a craftworld, or stay there for the majority of their lives.

Check how the Children of Thorns are presented in the Rogue Trader book. Just another Eldar Corsair fleet, just more excessive in their brutality. Well, a lot more excessive. Still - Eldar Corsairs. No distinction.

Its a Dark Eldar Kabal.

Pretty clear indication for me on what the Imperium, even most Rogue Traders, will know of the difference between Craftworlders, Corsairs and Dark Eldar.

On top of that, there is some fluff on how multiple raids by Dark Eldar were erroneously identified as being Corsair Eldar in origin even by the Ordo Xenos and that one Navy Department dealing with such matters, and I recall one case were DE actively attempted to disguise themselves as Craftworlders, though I can't find the source right now.

Check how the Children of Thorns are presented in the Rogue Trader book. Just another Eldar Corsair fleet, just more excessive in their brutality. Well, a lot more excessive. Still - Eldar Corsairs. No distinction.

Its a Dark Eldar Kabal.

Oh Ok. With that name I figured them to be renegade Biel Tan. (Wow, it is easy to mistake them for one another)