Color of the Hulk?

Originally, the Hulk was grey. Because the printers had trouble keeping the color consistent-- on some pages he was very dark and others much lighter-- Stan Lee changed his color to green starting with the second issue. No explanation was given.

For the next 25 or so years, whenever Marvel reprinted the first issue or showed a flashback to the origin, the Hulk was colored green from the start. It wasn't until #302 that the Hulk's original skin color was acknowledged in a single flashback image that many fans probably believed to be a mistake.

The Hulk returned to the grey color in #324 and remained that way for a few years before turning green once more. Grey skin's popped up a few times since then.

But typically the Hulk is green.