I don't think you are correct. The ET will indicate the position of the centre of the wheel rim to the mounting surface. The buyer would only need to purchase longer lugs if they use a spacer to keep the offset of the aftermarket wheel the same as the factory wheel.
We'll need to know the size of the rim (18" given the tires on them), width of the rim and offset of the rim. If the offset will require the use of a spacer then longer lugs are needed. If no spacer is require then factory length lugs should do. In the case of the OP he just wants black lugs to he'll have to buy them from ECS or somewhere similiar. As with what many have also posted, most aftermarket rims use conical bolt seats where the head of the lug meets the wheel so that will have to be factored into the lugs that are purchased.
I hope this helps.