Geoff,
It was never a bright white to begin with, Gibson called it "Classic White" so kind of a bit on the yellow side ( We all know there's more shades of white than any other color, right?) , the finish sweat stained and yellowed as I played the bass, especially live and it has it's share of honest wear, plus all the usual dings, dents etc. The color is rather uneven overall, when this started happening I was a bit upset about it as the bass was still pretty new, anymore, I just dig it.
Still makes noise too!