The color chosen will be the text (font) color for your tabs and accordion headers.
This setting in combination with the 'body text color' gives 2 color font schemes to your templates.
In the case of tabs, the active tab will get this font color, while the non-active tabs will get the 'body font color'.
Have a look at the color schemes demo for examples of how these colour combinations come together.
Header text color setting is a basic configuration option.
Here is the list of all basic configuration options.