>>"TrueColor" and "DirectColor" 
Thanks Nate,Hubert and Stephen ! 

On a more or less related note... 
I am running 4.2.0 on 1.6 using a 
patched version of the nv driver 
on a GeForce 2 Go chipset. 

I am having a bit of trouble with a program 
called IDL ( http://www.rsinc.com ). 

Having a look at xdpyinfo, it seems my default mode 
is TrueColor. A utility supplied with IDL indicated 
that it thinks the current mode is DirectColor. 

I wanted to be sure about what mode I was in so I elected 
to insert the statement ....

Visual "DirectColor" 

in my XF86Config file and tried to restart my Xserver. 
Unfortunately my Xserver puked with the message... 
 
(II) Setting vga for screen 0.
(II) Loading sub module "int10"
(II) LoadModule: "int10"
(II) Loading /usr/X11R6/lib/modules/libint10.a
(II) Module int10: vendor="The XFree86 Project"
        compiled for 4.2.0, module version = 1.0.0
        ABI class: XFree86 Video Driver, version 0.5
(II) NV(0): Initializing int10
(WW) NV(0): remove MTRR a0000 - c0000
(WW) NV(0): set MTRR f0000 - 100000
(II) NV(0): Primary V_BIOS segment is: 0xc000
(--) NV(0): Chipset: "GeForce2 Go"
(**) NV(0): Depth 24, (--) framebuffer bpp 32
(==) NV(0): RGB weight 888
(**) NV(0): Default visual is DirectColor
(EE) NV(0): Given default visual (DirectColor) is not supported at depth
24
(II) UnloadModule: "nv"
(II) UnloadModule: "int10"
(II) Unloading /usr/X11R6/lib/modules/libint10.a
(EE) Screen(s) found, but none have a usable configuration.

Fatal server error:
no screens found

I would normally guess that this is the truth and that nv won't
do DirectColor. But when I look at xdpyinfo I get a feeling
that at least it thinks DirectColor is supported.

Could someone suggest what the default behaviour is 
and perhaps a simple way to check for that behaviour...


xdpyinfo reports... 
<snip> 
screen #0: 
  dimensions:    1600x1200 pixels (542x406 millimeters) 
  resolution:    75x75 dots per inch 
  depths (7):    24, 1, 4, 8, 15, 16, 32 
  root window id:    0x3a 
  depth of root window:    24 planes 
  number of colormaps:    minimum 1, maximum 1 
  default colormap:    0x20 
  default number of colormap cells:    256 
  preallocated pixels:    black 0, white 16777215 
  options:    backing-store NO, save-unders NO 
  largest cursor:    32x32 
  current input event mask:    0x78607f 
    KeyPressMask             KeyReleaseMask          
ButtonPressMask          
    ButtonReleaseMask        EnterWindowMask         
LeaveWindowMask          
    PointerMotionMask        ButtonMotionMask        
KeymapStateMask          
    SubstructureNotifyMask   SubstructureRedirectMask
FocusChangeMask          
    PropertyChangeMask       
  number of visuals:    4 
  default visual id:  0x23 
  visual: 
    visual id:    0x23 
    class:    TrueColor 
    depth:    24 planes 
    available colormap entries:    256 per subfield 
    red, green, blue masks:    0xff0000, 0xff00, 0xff 
    significant bits in color specification:    8 bits 
  visual: 
    visual id:    0x24 
    class:    TrueColor 
    depth:    24 planes 
    available colormap entries:    256 per subfield 
    red, green, blue masks:    0xff0000, 0xff00, 0xff 
    significant bits in color specification:    8 bits 
  visual: 
    visual id:    0x25 
    class:    DirectColor 
    depth:    24 planes 
    available colormap entries:    256 per subfield 
    red, green, blue masks:    0xff0000, 0xff00, 0xff 
    significant bits in color specification:    8 bits 
  visual: 
    visual id:    0x26 
    class:    DirectColor 
    depth:    24 planes 
    available colormap entries:    256 per subfield 
    red, green, blue masks:    0xff0000, 0xff00, 0xff 
    significant bits in color specification:    8 bits