cosmic_cheese parent
Personally I found System 7.6/Mac OS 8’s Platinum to be a step up in usability compared to System 7 and before. The light mid-gray it used in most of its UI was pleasant and easier on the eyes than the stark white that made up the majority of the original Mac UI, but it was still plenty legible.
The System 7.0 UI appearance - before Platinum - was a mess. It was little more than a partially colorized version of the monochrome System 6 user interface; in fact, it mostly fell back to the System 6 appearance on machines with monochrome displays, like the (brand-new in 1991!) PowerBook series.
In a certain sense, Platinum was an attempt to reinterpret what Mac OS could have looked like if it had always been designed for a color display. It didn't just add color, like System 7.0 had; it added depth and texture to the interface which wasn't practical to display before. It also added a ton of new controls to the toolkit which previously didn't have standardized implementations or appearances. (For instance, System 7.0 didn't have a standard progress bar control - every application which used one had to provide their own implementation.)