Changed color scheme

Hello! About a year ago, inspired by Nick's video, I went to beta version 1.5_01 in order to look for herobrine. However, from the very beginning I encountered an inexplicable phenomenon: the color scheme of the version was changed. I searched the Internet for something similar, and found a post on VK, where the user encountered the same thing. We have one thing in common - we both play from a Mac computer. Later I discovered that this problem is present on all old versions, not just this one. I can still go to the old version and encounter this. I want to understand what happened and get answers - what happened and how to fix it? Thank you!