For the next Ubuntu release (20.04 LTS, to be released in April 2020), the Yaru maintainers are testing some important theme changes.
One of the updates involves using aubergine as a second accent color instead of blue, which didn't fit with the rest of the theme. Aubergine is now used for the GNOME Shell sliders and dialogs (active button/field), as well as for the Gtk progress bars, sliders, checkboxes, radioboxes and switches. The link color continues to be blue because aubergine is usually the color used for visited links, which would cause confusion.
The Yaru icon theme was also updated with brand-new folder icons, which are now predominantly gray, with aubergine/orange as accent colors.