Profiling was performed on volume slice drawing.  When colors were obtained for the voxels, the data in the corresponding map was requested so that if label data was being colored, the on/off status could be checked to to "turn off" coloring for the voxel.  The call to getMapData() was being made for all volume types but only needed for label volume types.  Now, the call to getMapData() is made only if a label volume is being colored and for non-label volume, performance is improved.
Moved a couple of computations outside of loops in volume slice drawing which seems to yield a slight improvement in performance.