Add all colors and styles to Assets Panel with a single click
Automatically adding color and styles to Assets by 1 click
It requires manually selecting the objects to add colors and character styles assets, but why it has to be manually selecting object? (performance concern?)
It could be done in an automatic way from the whole document level, by having a update button to while having a function to opt-out from a object by object basis. And this integrates the Color used in a design with the swatch library.
The current function requiring manual selection of object.
You have to manually do it every time a new UI is created, but it is risky as you might forgot or miss out some in the selection process.
That's the reason try to propose an automatically update of colour palette (or with a refresh button if needed)
Mathew Izzard commented
If you right click the art-board you can add all assets that way, it's not one click, but it's pretty close.