If you have the borders disable per hotbar, I'm not sure, but I know when you have it enabled, it's actually controlled via the XML file.
See the red hex color:
Code:
<IconBank BackgroundOpacity="1.000" Dragable="true" font="/TextStyles.Normal.NormalStyle" framecolor="#B5935A" iconframepadding="0" iconpadding="0" iconstyle="/IconStyles.button" Location="11,0" Name="Icons" PackSize="a,a" renderframe="true" renderoutlines="true" ScrollExtent="384,32" Size="384,32" textcolor="#C3C3C3" textmargin="2,-1,2,-2" treatasbutton="true" />
Glad you like the mod. Enjoy changing the color how you see fit
This would be something that would be possible for me to code into a possible Mod Option window in the future. *noted*