Can you tell me how to modify the color of the category bar color.
Here is the image:

How to change its color.
This is actually an image,
You should check out /default/images/theme/main_block.png
There are basically two parts in index.css to change:
div.cat_bar {
background: url("../images/theme/main_block.png") no-repeat scroll 0 -160px #99ABBF;
height: 31px;
margin-bottom: 1px;
overflow: hidden;
padding-left: 9px;
}
h4.catbg, h4.catbg2, h3.catbg, h3.catbg2, .table_list tbody.header td.catbg {
background: url("../images/theme/main_block.png") no-repeat scroll 100% -160px transparent;
padding-right: 9px;
}
You can replace them with another image or you can use css to change its color.
In my new Revamp SMF theme, I change the first part to :
div.cat_bar {
background-color: #556AB0;
border-radius: 5px;
box-shadow: 0 2px 6px rgba(0, 0, 0, 0.5), 0 1px rgba(255, 255, 255, 0.3) inset, 0 10px rgba(255, 255, 255, 0.2) inset, 0 10px 20px rgba(255, 255, 255, 0.25) inset, 0 -15px 30px rgba(0, 0, 0, 0.3) inset;
height: 31px;
margin-bottom: 3px;
overflow: hidden;
padding-left: 9px;
}
And I just cleared the second part so that it won't be redundant, like this:
h4.catbg, h4.catbg2, h3.catbg, h3.catbg2, .table_list tbody.header td.catbg {
padding-right: 9px;
}
It is really up to you on how to change it.
Note: box-shadow is will change a simple color to make it look like an image; while border-radius will make it curves.