VDU 19 API                                                                  Supported on
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Logical colour:
             VDU 19,<128 ,p,r,g,b       set logical colour
             VDU 19,128+n,p,r,g,b       provisional: set alpha channel colour
             VDU 19,-1   ,p,r,g,b       set border colour (-1 is sent as CHR$255)

Physical colour:
  0+RGB      VDU 19,l,%00000bgr,r,g,b  steady physical colour               All
  8+RGB      VDU 19,l,%00001bgr,r,g,b  flashing or bright physical colour   All
 16+action   VDU 19,l,%0001xxxx,r,g,b  RGB colour                           RISC OS, BBC ext, DOS, Win
 32+RGB      VDU 19,l,%0010ebgr,r,g,b  first flashing physical colour                BBC ext
 48+RGB      VDU 19,l,%0011ebgr,r,g,b  second flashing physical colour               BBC ext
 64+action   VDU 19,l,%01xxxxxx,r,g,b  reserved
128+action   VDU 19,l,%100yyyyy,z,x,x  CPC: 5-bit physical colours y and z  CPC
255          VDU 19,l,%11111111,r,g,b  DOS: 6-bit RGB colour                DOS

This gives the following implementations:
  0          VDU 19,l,%00000000,r,g,b  RGB colour
  0+RGB      VDU 19,l,%00000bgr,0,0,0  steady physical colour
  8+RGB      VDU 19,l,%00001bgr,0,0,0  flashing or bright physical colour
 16          VDU 19,l,%00010000,r,g,b  RGB colour
 17          VDU 19,l,%00010001,r,g,b  first flashing RGB colour
 18          VDU 19,l,%00010010,r,g,b  second flashing RGB colour
 24          VDU 19,l,%00011000,r,g,b  border RGB colour
 25          VDU 19,l,%00011001,r,g,b  pointer RGB colour
 32+RGB      VDU 19,l,%0010ebgr,r,g,b  first flashing physical colour
 48+RGB      VDU 19,l,%0011ebgr,r,g,b  second flashing physical colour
 64+action   VDU 19,l,%01xxxxxx,r,g,b  reserved
128+action   VDU 19,l,%100yyyyy,z,x,x  CPC: 5-bit physical colour
255          VDU 19,l,%11111111,r,g,b  DOS: 6-bit RGB colour