Hello Ray,
On the "Organ settings | Rank voicing ..." screen It's definitely still there in v8 (I just checked for good measure), but since v5 it's named "All perspectives: overall: brightness (dB)" (and there are also four per-output-perspective brightness adjustments).
However, note that (as in all previous versions) brightness adjustments aren't available if you've ticked the "Disable harmonic-shaping filters" option on the "Organ settings | Organ preferences | Audio engine" screen tab, since those are the filters needed for adjusting brightness.