If I fire up X on my SS20 (has a cgsix) running NetBSD-1.6, 
xdpyinfo ouput includes:

name of display:    :0.0
version number:    11.0
vendor string:    X Consortium
vendor release number:    6300
maximum request size:  4194300 bytes
motion buffer size:  256
bitmap unit, bit order, padding:    32, MSBFirst, 32
image byte order:    MSBFirst
number of supported pixmap formats:    2
supported pixmap formats:
    depth 1, bits_per_pixel 1, scanline_pad 32
    depth 8, bits_per_pixel 8, scanline_pad 32
keycode range:    minimum 8, maximum 132
focus:  window 0x140000e, revert to PointerRoot
number of extensions:    14
..
..
screen #0:
  dimensions:    1152x900 pixels (325x254 millimeters)
  resolution:    90x90 dots per inch
  depths (2):    1, 8
  root window id:    0x2a
  depth of root window:    8 planes
  number of colormaps:    minimum 1, maximum 1
  default colormap:    0x21
  default number of colormap cells:    256
  preallocated pixels:    black 1, white 0
  options:    backing-store YES, save-unders YES
  largest cursor:    32x32
  current input event mask:    0xd0001d
    KeyPressMask             ButtonPressMask          ButtonReleaseMask        
    EnterWindowMask          SubstructureRedirectMask PropertyChangeMask       
    ColormapChangeMask       
  number of visuals:    6
  default visual id:  0x22
  visual:
    visual id:    0x22
    class:    PseudoColor
    depth:    8 planes
    available colormap entries:    256
    red, green, blue masks:    0x0, 0x0, 0x0
    significant bits in color specification:    8 bits
  visual:
..
..
  visual:
    visual id:    0x26
    class:    TrueColor
    depth:    8 planes
    available colormap entries:    8 per subfield
    red, green, blue masks:    0x7, 0x38, 0xc0
    significant bits in color specification:    8 bits
  visual:
..

I'd like to see if TrueColor makes it possible to look at pictures
without shocking grain and colorization.  But none of the man pages
I've looked at and not even "strings Xsun" give a clue as to how to do
so.

Clues welcome.

Thanks
--sjg