59 isn't dark, it just doesn't have much in the way of midrange and is tubby. A popular thing to do is swap the magnet to an A4, cures those things. An A2 59 is cool too, but way more vintagey.
JB is all upper mids and highs, the low end and low mids are understated, when stuck in a darker/bassier guitar it can sound real loose and really just wrong. Kinda gets a bad rap because all the manufacturers stick them into everything (ESP). It usually sounds best in brighter guitars, with 250 pots, which is totally counterintuitive.
They could sound great, but I wouldn't count on it. They really should be putting custom/59 sets in those guitars.