drupal 7 lack of understandig location of bartik's color.css
The Bartik theme has support for the Color module, which is a module that allows themes to change the color used in their images, or in their CSS style files basing on a schema defined in the theme settings page.



When the selected color set is not the default one, color_scheme_form_submit() generates the files that will be used for the theme. The files you have seen inside the sites/default/files/color directory are the ones generated from the Color module, and that will be used for the theme. The files in the theme directory are the ones used when the color set is the default one.

As side note, if you are editing the files used by a theme that supports the Color module, you need to disable, and then re-enable it, or the files used for the theme could still be the old ones.