Category Highlight Color
You can select a highlight color for every category. Wherever this category shows up, this color will be its highlight color. For changing this color follow below steps.
Go to Posts → Categories, find the category you want and edit it.
Now scroll down to Better Category Options meta box. The first option in Style tab is “Category Highlight Color”, select the color you want and save the changes.
Category Top Posts Background (in archive page)
Read more about Category Archive page options; here we just want to change background color of top posts in category archive page. Go to Publisher → Theme Options → Color & Style → Category Top Posts, now change the background color.