Why was Dr. Manhattan blue?

Question

Dr. Manhattan clearly had some control over his appearance. The hydrogen atom on his forehead was by choice, and he adjusted his blueness for the cameras when he was told it was too bright.

Wikipedia claims without citation that Cherenkov radiation was the reason for his skin color. But he had seemingly very powerful control over matter. Could he have appeared any color he chose, including like a regular human? His super-powerful appearance was a useful part of his public persona, but it seems like when he was in private (especially with Laurie) he would want to look as human as possible.

Did he not have this ability, or did he choose not to use it?

Answer 1

From the interview and quotes from Comic Con's “The Physics of Watchmen — or Why So Blue Dr. Manhattan.” by University of Minnesota physics professor Jim Kakalios who teaches a class called “Everything I Know About Science I Learned from Comic Books.” (He also wrote “The Physics of Superheroes”), he speculates:

Could be because of an electromagnetic shock front which gives off energy in the ultraviolet or the blue portion of the spectrum. He has to reassemble himself on the removal of his intrinsic field. He is constantly generating, pulling up stray electrons out of the ground to keep his atomic balance right. Some of these electrons are leaking off creating drain off radiation. By adjusting how fast they’re going he can adjust the hue and intensity of his glow.

This coming from a comic book geek AND Physics college professor, I'll take it as close to authoritative as it can get :)

Answer 2

Watchmen co-creator Dave Gibbons said in a Q&A that he wanted Manhattan's blue skin to represent a sort of barely-contained "electrical energy or atomic energy" in the reader's perception.

Dave Gibbons: Actually, Dr. Manhattan is not the only blue character that I’ve created the look of. I co-created a character called “Rogue Trooper,” who appeared in the British weekly comic 2000 AD, and he had blue skin. Rather reptilian skin.

I like blue because it kind of reads the same kind of tone as skin, or as Jon Osterman’s skin would’ve read. But it’s obviously not real human skin. Green makes you think of bug-eyed monsters like aliens, yellow is too strong a color, red looks artificial. A light blue kind of looks like skin tonally, but looks completely different from it in its hue. I think it also relates to the way you might visualize electrical energy or atomic energy. That it’s a kind of blue, pure energy. A cold energy, unlike fire or flame, which is what a red color would make you think of.

That was really why I chose blue. I think I just came up with the color and Alan incorporated it in the story. It didn’t make a lot of difference in the story which color he was, but I think visually, that blue was the right color for him. And it worked very well with the colors of the costumes of the other characters, and also the fact that John Higgins and his color palette didn’t use a lot of blue as a background color. So I think for that reason, it worked.

_{^{Watchmen Secrets Revealed}}

That the blue glow was caused by a form of Cherenkov radiation was (to some extent) confirmed by Gibbons in a round-table discussion on NPR.

Dr. KAKALIOS: Well, yeah. Actually, I - see, I lost a bet. I thought that you had chosen blue for the color of Dr. Manhattan because whenever you see images of nuclear reactor piles underwater, you see them emitting a blue glow, and…

Mr. GIBBONS: Yeah.

Dr. KAKALIOS: …blue light is from the fact that they're emitting high-energy electrons which create an electromagnetic sonic boom called Cerenkov radiation, which is in the blue, ultraviolet portion of the spectrum.

If Dr. Manhattan were blue because he was emitting these high-energy electrons all the time because he had reconstructed himself atom by atom, well, he probably would be giving people cancers.

Mr. GIBBONS: Right.

_{^{Does 'Watchmen' Hold Hidden Physics Lessons?}}

Answer 3

I think it might be traced to this: As he witnessed the first detonation of a nuclear weapon on July 16, 1945, a piece of Hindu scripture ran through the mind of Robert Oppenheimer: “Now I am become Death, the destroyer of worlds”. Hindu Gods are often depicted as Blue-skinned.

Answer 4

For a more aesthetic reason, Blue is considered in many cultures, particularly western ones, to be a colour of innocence and peace.

If you were going to pick a primary colour for your skin and you wanted as few negative connotations as possible, blue is culturally your best shot, particularly in America.