Thanks! I'm still pretty new to mouse reviewing, but I tried to do my best to be rigorous in testing methodology.
To answer your questions...
1. The color on the Zealot Jr. is not swappable. In fact, there's no software for the mouse whatsoever; sensitivity and polling rate are adjusted by switches on the bottom of the mouse, but that's it as far as configuration goes. The original Zealot has more flexibility, since it does have software (as well as the ability to display more colors), different profiles, etc.
2. It's hard to tell build quality for sure on a newly arrived product, but it certainly feels solid, with no creaking, rattling, or other signs of fragility. My original Zealot has survived 9 months of intensive use and, aside from a couple of aesthetic blemishes where a bit of the electroplated coating on the side grips has worn off, still seems as good as new-- or perhaps better, now that the braided cord has had a chance to break in and gain a little extra flexibility. If the Jr. is put together as well as the original, it won't be breaking anytime soon.
3. Nope, no side buttons. The original, on the other hand, does have a thumb button-- by default, it cycles the sensitivity, but you can set it to whatever you want. At the moment, I have it set to "Alt", so that I can do alt + scrollwheel for forward and back. Can't do that with the Jr., though, since there is neither a side button nor any software by means of which to set a function for one.