Both default dark themes introduced with that add-on both got strong blue hues. As we currently only support a single night and day theme, I’d be concerned many people don’t like that particular hue. That’s why
Of the two light themes I prefer Catpuccin, because it looks more neutral. It does however lighten the window background even more than my PR does (#fafafa vs #f4f4f4). As @dae said:
One thing I took note of was the main window toolbar and button design changes. As the main view is just a huge blank canvas right now, it makes sense to spread elements out a bit and use drop shadows instead of harsh borders for buttons. But that’s a bit off-topic, because we’re talking about colors in this thread. See Brainstorming for modern UI [Anki 3.0] for more discussion on the UI itself.