Sad...replying to my own post, but it made more sense than an edit...
Now I see why I had no clue what this was. I don't do social media (unless you count the DIS). Here's two postings (on a DIS forum, no less) I found:
Edit: apparently it's just a regular purple wall in tomorrowland by monsters inc and tomorrowland terrace. Doesn't mean anything, just a social media thing started by someone. Guess a couple people liked the purple wall background then others just followed and did the same. I don't get it either
Some things start off kind of stupid and then end up actually being a thing that sticks. The purple wall is one of them. It’s located in Magic Kingdom near The Laugh Floor. It’s a pale purple blank wall that really doesn’t look like anything special. Except it is. I thought at first it was only because it had become popular to post a selfie or a full body picture of yourself at the wall. And yes. It is mostly that. But, it also happens to photograph really great. It’s a flattering background color on everyone, there’s good indirect lighting there, and its just out of the way enough that you don’t have an audience watching you. Meaning you don’t feel as dumb taking 487 selfies to get one that’s actual worth posting to Instagram. (Or is that just me?) It has it’s own Instagram account, and is also featured quite a lot on another Instagram account (WallsofDisney) that highlights the walls in all Disney Parks that make great photo backdrops.
So, if I stopped after reading the first post, it would have still been rather strange to me. After reading the second, it would seem there actually is some purpose (other than a social media thing/craze) in that it makes a good backdrop for photos.