>> The PMAG-JA listing on the web page is slightly wrong.
>> 
>> The PMAG-JA is an unaccelerated _Direct_Colour_ board, not _True_Colour_.
>> 
>> The difference being that Direct Colour boards have a programmable palette,
>> whereas the True Colour boards don't.

One Digital document states that TX board is a 'true-color' system.

	DECstation 5000 Family Graphics Technical Overview 
	EC-N0663-51

In one of pages describing excellent technical references on how
framebuffer circuits are constructed, page-11 says;

  A 24-bit system that has no color lookup table (such as TX option) is called
  a true-color system.  The 24 bits at each pixel are partitioned into tree
  8-bit fields, which directly determine the RGB values for the pixel.

The next paragraph refers to PXG as a psuedo-color system (8+8+8).

Another  excerpt from page-12;

  The TX graphics option has been designed especially for use in conjuection
  with the DECvideo multimedia options, discussed in Section 5.  It provides
  a socket for the DECvideo/PIP livevideo daughter card.

  The TX resolution is 1280x1024 and its pixel depth is 24+8+1.  More
  specifically, the TX contains a 24-bit true color frame buffer and an
  independent 8-bit, color-mapped frambuffer.  The contents of the single
  bit plane determines, for each pixel, which of the two frame buffers
  determines the color of that pxiel.  Therefore, either the 24-bit iamge
  or the 9-bit image may be used as an overlay on the other.  The 24-bit
  frame buffer may display realtime video from the DECvideo/PIP card.

In the aspect of color capability, TX seems a straight application of
Brooke Tree Bt463 RAMDAC. 

Tohru Nishimura
Nara Institute of Science and Technology