Why did my cornsnake get pale?

Just from the brief description, it does sound like your new snake is going through a shed cycle. You should see his coloration return to normal in a day or two and then he'll shed soon afterward. If you don't have one already, you should provide him with a humidity hide. It will help prevent any potential shed problems associated with low humidity. If he sheds completely in one piece, it's a safe bet your husbandry is spot on. :)

Hope it helps.

For all the details you provided it all points to the fact that it is in a shed cycle.. and there is nothing to be worried about.. in a couple of days the colors should return to normal and the snake will shed in a couple of days after that.. just make sure u keep the humidity 10 % higher then normal times or 70% in total.. it will help the snake shed easily..

I would also say he's getting ready to shed. Did you notice his eyes turn very blue. My little guy's eyes only stay blue for about a day before the shed. And yep, you're looking for a one-piece shed (including eyes).