If custom there may be code in CSS controlling it. You may want to check in the ACP -> Style Properties -> Message Elements -> User Generated Link (Hover) and see if there is a background gradient/image applied otherwise and try that.
If custom there may be code in CSS controlling it. You may want to check in the ACP -> Style Properties -> Message Elements -> User Generated Link (Hover) and see if there is a background gradient/image applied otherwise and try that.