Zapped,
You are talking about two different rules. If the main bonding jumper in the service equipment is a screw, that screw must have a green head. See 250.28(B). The purpose of this rule was to make it easier for the inspector to see if the main bonding jumper was installed. The other rule in 250.8 prohibits the use of a "sheet metal screw" to connect a grounding conductor to an enclosure. The only problem with this rule is no one knows what a "sheet metal screw" is.
Don
