This link has a tutorial on ascertaining the color codes for an unknown HB. Add in the magnet test for N or S and you have all the info you'd need (Also note what JohnH said, that N and S are relative only, as mfrs differ on how they assign it)
If you ever really need to know the absolute magnetic polarity of anything, all you need is another magnet whose absolute magnetic polarity is known. This thing does that, I suppose, but it looks kind of silly.
There's no real good reason we ever need to know the absolute polarity of our pickups. Even if you're one of those guys with piles of pickups they swap in and out and around all the time, you just pick one as a reference. Relative polarity is all that matters.