I appreciate TB9 user zenrain's custom themes he's been sharing, but I was embarrassed to admit I never quite figured out how to import them, spending a lot of time looking through my computer's file system for a place to drop the files and have them appear inside TB9. After reading zenrain's posts, the proper methods began to make sense, but I thought one simple explanation might make it easier for others trying to use shared themes. Please correct and simplify at will.
When you manually change color settings in theBrain's Brain Theme panel, it causes the theme Custom Settings to appear at the top of the list. This allows you to name and save the Custom Theme, which then appears as an option for all brains.
To grab a theme that someone has shared, you'll need to either manually enter their settings, or import a .brz of their brain with the desired theme. For sharing purposes it only needs a single thought. Once imported, if the colors don't match any of your existing themes, Custom Settings will again appear at the top of themes panel. Save and name appropriately, and it will be available to all brains.
iMac (Retina 5K, 27-inch, Late 2015)
3.3 GHz Intel Core i5
32 GB 1867 MHz DDR3