By default, the skin use the "Combobox border" for most "edit borders"
but if you want to use a solid color instead, open the skin .UIS or and .SSS files with Notepad (they're) located in your skin folder) and add these lines:
[Edit.Border]
EdgeColour=
On "EdgeColour=" se the color from the skin that you want to use, exemple:
[Edit.Border]
EdgeColour=5