How to turn off orange underline for column header?

I have turned of sorting following the example of thread /javascript.forum.1470.12/disable-sort-feature.html.

I then wanted to turn off the orange underline for the column header which does not make sense in my eyes if there is no sorting. I found the following thread: /javascript.forum.398.4/tweek-the-column-header-row.html But if I follow the advise and for example just for testing use a bottom border color of green, I now see two colors, still the orange and above the green line.

There must be some other style I need to overwrite, but I cannot spot it. Any idea which one?

Thanks in advance.

I am still not able to turn of the orange underline in the xp style. Has someone an idea how to accomplish that?

A possible solution could be here (?)
/javascript.forum.398.4/tweek-the-column-header-row.html

Find and comment out these 2 lines in grid.css:

.active-header-over{border-color:#f9b119;background:#fcc247!important;}
.active-header-over .active-box-item{border-color:#f9a900;background:#faf9f4;}

This will remove the orange "lines" (actually borders)

Does anyone know how to only change the color of the bottom border not the top/sides?

you can change any of the border parts by using the following nomenclature:

border-bottom-color : red;
border-top-color : green;
border-left-color : yellow;
border-right-color : blue;

in fact, with FireFox (or it might have been Opera) you should break out your border assignments into the 3 parts since it has troubles with:

border : 1 solid black;

You have to use:

border-style : solid;
border-color : black;
border-width : 1;

besides, this is more readable anyway.