Borders > Colors
Borders is using color schemes to set colors, a helpful way to easily adjust the colors of entire sections on the fly. You can set many color schemes and use them in different sections, giving your store's a really unique design.
See the screenshot below for the anatomy of a color scheme:
All sections start out with the first color scheme, so if you want to change how all sections look at once, just edit the colors within Scheme 1 and all sections will follow.
However, at any point you can choose a custom color scheme for almost any given section. You will notice that most sections have a Section design part at the end of their settings, which allows you to play with the design.
Once you select a color scheme for a section, it will not be affected by the first color scheme.
Default color scheme
There are also a lot of sections that don't have color scheme options, mostly page sections, such as articles, 404, customer accounts, etc. You can change the color scheme of these pages through the default color scheme setting, which is set at the first one, so it may be something that can be left unchanged if you're editing the entire design through the first color scheme anyway.
Body background
At the end of the settings list you have the body background option which will set the color of the store's background, but please note that this is visible only if your store has margins or features a fixed width design.
At the end, you can change the color scheme for all the drawers.