poor display resolution

[Morris Trimmer]

    We have imported scanned photos and everything seems fine 
except that when we display them there seems only to be 8 shades of 
grey while we have 16 categories.  We intend to rectify these and 
map on them with digit.  It would be very helpful if we could get all 
shades shown on the display.  Any suggestions?  
  The color file ( grass4.1/data/'location'/'mapset'/color/'rasterfile') 
shows the 256 colors evenly devided among the 16 categories.  Also 
when I display the photo with the xgrass 'Display Tool' the other 
shades are visible.  Why does my d.mon display monitor only show 
the eight?  Can I change it?  Will I have this problem with color photos 
as well?
  Thanks tons.