public function forcebw()
{
// XXX: won't work yet
/*
vboxes = this.vboxes;
vboxes.sort(function (a,b) { return pv.naturalOrder(pv.sum(a.color), pv.sum(b.color) )});
// force darkest color to black if everything < 5
var lowest = vboxes[0].color;
if (lowest[0] < 5 && lowest[1] < 5 && lowest[2] < 5)
vboxes[0].color = [0,0,0];
// force lightest color to white if everything > 251
var idx = vboxes.length-1,
highest = vboxes[idx].color;
if (highest[0] > 251 && highest[1] > 251 && highest[2] > 251)
vboxes[idx].color = [255,255,255];
*/
}