Are there cryptographic schemes that mask as unencrypted traffic? Are there cryptographic schemes that make encrypted traffic look like unencrypted traffic?
Well there is Steganography like Richie said in the comments it is essentially the art of hiding messages. This being said it is not comparable to any encryption algorithm (like AES) security wise. Though there are tools for steganography which requiere keys so they encrypt data before they hide it but this is not the essence of steganography since steganography is only about hiding the message.

If you are looking for a way to hide your messages this would be sufficient, if you want to properly encrypt it you can do that before hiding the message.

If you're looking for only an algorithm which mutates a text to a different text i'm afraid your out of luck. a home brew of a pseudo random pad where you make the key in such a way the words change like this:

plaintext: Welcome
key: kkdbnma
cipher text: Goodbye


Though this is insecure, it might be fun to play around with but it is not to be used in real life situations!

EDIT:
as pointed out Robert NACIRI there is also the use of subliminal channels as described by this wikipedia article. As it suggests it hides messages inside normal communications, read it through for examples and a better sense of how this works. It's quite interesting.