Since nobody is answering this issue, I'll step in.
Those lots have been sold or abandoned. I'm not sure how it started, but Wallet and some others ended up having their lots sold and they were multicolored afterwards. I believe each user intentionally spray-spammed their build rainbow, just for the hell of it and it caught on. No one person is responsible for this, you obviously aren't familiar with the mechanics of the mod or Blockland for that matter if you think someone can just go around colouring peoples businesses.
Since then some people have been painting their builds that way, almost all of the lots sold but one or two of them remain owned. Its turned into a kind of fad I think.
