I didn't get your error running Vikka's code. You can also try:
Code:
Sub BorderColor()
Dim oBrdr As Variant
Dim MyColor As Long
Application.ScreenUpdating = False
MyColor = 10027008 'InputBox("Specify color code", "Border Color")
For Each oBrdr In Selection.ParagraphFormat.Borders
With oBrdr
.LineStyle = wdLineStyleSingle
.LineWidth = wdLineWidth050pt
.Color = MyColor
End With
Next oBrdr
Application.ScreenUpdating = True
End Sub