Main Theme Color - color that is set throghout the Theme (red is default color for TreeBeard Theme). Once you change the color please not that not all aspects of the site will change (some color will still be red). This is because on some parts of the Theme shortcodes are used. You need to change this manually as it gives you much more freedom in color selection (it can be anything independant from theme's main color).
Color of Main Titles of blocks (on home pages) can be changed directly in the Block Start block in the Page Builder. This means you can have different colors of Titles for each block, making it very versatile.
Lower Border Color - color that is set for lower borders (buttons, etc.)
Boxed version - if you need a boxed version, check it here and then set the background color or image.
Custom Style - if you need to change CSS for certain parts of the Theme you can add it here (so you don’t have to edit the style.css).