In my recent exposure to g&l basses,i’ve found both my lb100 and the jb2 to have a razor sharp sound. That absolutely seems to bring out the best with flatwound strings. My lb100 had factory nickle roundwounds on it when i got it,and I didn’t like the sound at all...now has a set of Chromes and sounds great. The jb2 came with Labella flats,and it sounds fab with those. I don’t know if you were using roundwound strings on yours,but it just seems like they can be pretty harsh sounding.
Chromes on an LB100 are just magic.
Getting back to the burst-on-the-back thing, there's really no good reason for wanting a back burst to go with the front since you won't see it on stage. So black-on-the-back should be just fine. That said, though, G&L does such beeootiful bursts, that I love have a great uninterruped expanse of burst on the back to look at when I handle the instrument. That's just me.

However...there's 13 sets left at Amazon for only $26 ($40 off):