I'm thinking of swapping my pickups around but one of the swaps will involve installing a set of zebra BKPs in an all black guitar which I'm reluctant to do on aesthetic grounds. The easiest fix that I can think of is to cover the pickups with plastic (EMG style) pickup covers. There's a good demo online courtesy of BKP showing how nickel covers effect sound but would I be right in thinking that plastic covers are magnetically transparent and as such will have no effect on the overall sound?