Long, two-part interview with Louise Simonson and Walter Simonson. Here's what they said about the designs of Apocalypse and Archangel:
AIPT: This wasn’t one of my planned questions, but while I have you both here–what’s inside the tubes that are part of Apocalypse’s costume? In a past edition of X-Men Monday, X-Men Senior Editor Jordan D. White suggested they might be energy conduits.
Walter: Oh, out of his elbows to his back?
Louise: I don’t have a clue. What about you, Walter? Anything he wants to be there, I suspect.
Walter: I think it’s green ichor–thats what it is. But other than that, I haven’t got a clue. They look really cool.
...
Walter: It was. And I will tell you the truth, I have no idea where that design [for Archangel] came from. I hate to say that because it’d be interesting to know. I can give you chapter and verse for Beta Ray Bill’s design and name, but I cannot tell you where the Archangel design came from. I don’t remember looking at stuff. I mean, I look at a lot of stuff, especially when I’m trying to design something–I’ll go out and just look at stuff for inspiration. I have no idea. Maybe the piping on Patrick McGoohan’s jacket in The Prisoner from 1967–but I don’t think that was it.
Also:
Mostly, you expected to put this stuff out and have it evaporate the following month when the next issue of that book came out, and then that issue would evaporate. And there was no real sense, at least not for me, of creating material that was going to be around longer than the newsprint it was printed on.
So I don’t think I created any characters with an expectation, “Oh, this is going to be the next big thing.” I just tried to create the characters that I thought would work in the comic and it helped me tell a good story, knowing that those stories would evaporate when the issue went away.