Hello! In Cassio theme colors are adjustable via Customizer -> General Style -> Colors panel:

These colors are used in pre-defined color themes on Elementor sections as mentioned in this article: https://docs.artemsemkin.com/cassio/wp/elementor/extended-section-widget.html#configuring-color-presets 

When you change color theme of the outer section, it automatically adjusts colors for the inner elements, like text color, decoration elements, background, etc. There is no direct color adjustment available from the widgets themselves.