I want to get some black humbucker covers for my guitar, but I have some questions about them first. The main question I have might be stupid, but it seems like it could happen. Anyways, do you lose any power when you have humbucker covers on your guitar? It seems like it'd make the guitar have a lower volume, or have a worse tone, but I don't know if it does or not. So I'm just wondering if anyone could tell me if it effected their guitar any.
Randy Rhoads & Dimebag
Arguably the tone will be a bit mellower with a bit less treble exaggeration (I've yet to see any documented proof of this, but everyone has an opinion).
ESP LTD EC-256 and a Fender Deluxe VM
^^No proof, but it seems thats what most people say, I think the tone itself may differ slightly, but it wont be 'worse' putting a cover on it will not make it sound like crap (unless it was crap before hand of course).

If im correct you have to take the PUPS out of the body/pickguard (im not sure what guitar you have) then solder the covers directly on to the PUP, then put back in.
when you put covers on your pickups, you have to be sure to wax pot them, if you dont then there will be pockets of empty space inbetween the pickup and the cover making it feedback. So you have to fill in the spaces with wax!

IMO covered pickups have little-no effect on the sound of the pickups.

Gibson Les Paul Studio w/dirtyfingers pickups
Gibson Joan Jett Melody Maker
VOX ac30 head
Marshall 1960 4x12 cab
Fender Hot Rod Deville
Rad, I have a Jackson RR3, Crimson swirl, one of the pro edition ones that come with a Seymour Duncan JB in the bridge and a Jazz in the neck. Maybe they're all like that now, but when I got mine, about a year and a half ago I believe, there was RR3's that had Duncan Designed pickups, and not the JB and Jazz. I love it, it's my pride. I thought that black covers would look good on top of the crimson swirl finish.
Randy Rhoads & Dimebag