The rumor of the "Four Barons of Hell" is one that has been floating around in Neon Genesis Evangelion circles for ages, before even 2000.
While this rumor is supported by several Evangelion fansites (1), and even collegic papers (2), not only is there no evidence of the appearances of the Evangelions being based on these creatures, there's also no evidence they were ever part of any religious texts, especially Judeo-Christian ones.
A quick google search will lead you to endless Evangelion and Doom websites, but no religious ones. So, where did the idea of the Barons come from, and if not that Barons, what are the Evangelions based on?
"Lost", a member of Animeboards.com, makes a suggestion that the Barons of Hell (3) came from Inferno, Dante Aligreli's classic novel about a journey to Hell. However, a full scan of Inferno gives no mention of the words "Barons of Hell", nor does looking for a description of the Barons lead to anything. Inferno is out.
A common mistake, the the four Barons of Hell are the same as the Bible's Four Horsemen of the Apocolypse leads to several mistaken references to the Bible's Revelation. However, the Horsemen don't fit the description of the Barons at all, and can be eliminated as well, including the Apocryopha, as searched in by Animeboards.com's "baragon21" (4).
"Shinchan911" provides more of a hint at the origin of the Barons of Hell, but can't provide any definite proof:
"... taken from the four Elder gods of Babylon. There names are: Anu, the God of Heaven. Enlil, the God of Air. Ki (aka Nintu), Goddess of earth, and Enki, God of Water. They are called the four Creating Gods, because apparently all gods came from them. And as I said before Judeo-Christianity turned these four creating God into the Four Barons of Hell." (5)
Shinchan911 locks out the four 'Creating Gods' with his next statement ...
"But after intense research, I found no trace of anything about them having 'Four Eyes' or a 'Horn' or any description what so ever." (5)
It's now become widely believed that the Barons of Hell don't exist in any religious text, and that the quote is a hoax by an Evangelion fan. But if this is the case, where did Evangelion get it's color-scheme, and shapes and such?
One answer comes from "Mecha Designer" Ikuto Yamashita (6), who writes:
"'So, why did Evangelion wind up with that shape?' I figure that from now on, I will hear that question countless times. The director instructed me to make, 'the image of a demon.' A giant just barely under the control of mankind. I get the feeling I've seen that correlation before... The image I had for the design concept was the fairy tale, Gulliver's Travels. Enormous Power Restrained.
And I wonder if what I came up with was what the director was driving at. Or was I simply come unprepossessing unknown leading a charmed existence. What I came up with was a giant that looks like a relief on a wall. To achieve my selfish desire, I happily discarded the efficiency and feeling of giant size that you can guess at by sight alone."
Another answer, the best in my opinion, comes directly from the Creator, Director, and Mastermind behind Neon Genesis Evangelion, Hideaki Anno himself in an interview with Aerial Magazine's Amos Wong:
"There's a monster in Japan called the Oni; it has two horns sticking out of its head and the overall image of the Eva is based on that. I also wanted to give the impression that beneath this 'robot monster' image is not so much a robot, but a giant human." (7)
The main design influences with the Evangelions are the Japanese demons Oni, and not at all the alleged four Barons of Hell.