Hello,
1) If you want to show only subcategories of the current category then enable option “Only show children of the current category”, this is default WC option for the categories widget. But keep in mind that this widget is the list of categories, it’s not the filer widget! To show list of categories and filter by category is a little bit different things especially if you want to combinate it with other filter widgets.
2) By default color swatch widget displays all the colors
But this is a good suggestion to show only colors available for the current category. I’ll pass this task to our developers to improve it. They will be able to check on Monday. Provide FTP access to your site to implement it for you once they finish.
Regards