The ShopSite VAR tags such as [-- VAR.sc_banner_bg_color --] are defining a variable which can be used in other places in the template or in some other template that is active at the same time, (I.E. during the publish, displaying the shopping cart, doing a search etc). The value of the variable will be kept in memory and used in multiple places. What you need to find is where [-- VAR.sc_banner_bg_color <xyz> --] (where <xyz> is some text or a number) is located and see what is being specified for the <zyz>
I looked through the files and see that the declaration of VAR.sc_banner_bg_color is in classy_sc_vars.sst: and is
[-- VAR.sc_banner_bg_color STORE.SC_ShadeColor --]
So the banner bg color is being pulled from the STORE.SC_ShadeColor which is configured on the Commerce Setup > Order System > Layout > Table Shade Color: . and just changing the color there should affect the pages in your store or cart where that VAR is used. (Note: you could also replace the VAR statement [-- VAR.sc_banner_bg_color --] with just a color value, (such as #FFAABB ) if you want to do that but it wouldn't be as flexible as using the VAR
It can be a little difficult to find where a VAR is initially set or changed but by going through the files that get included using the [-- include <filename> --] format and looking for ones that include "vars" in the file name would be where I would start.
You can find what all the tags mean by going to the custom template specification at
http://www.shopsite.com/help/10.1/en-US ... .spec.html
or a concise format at
http://www.shopsite.com/help/10.1/en-US ... et.sc.html