#include <graphics.h>
void setrgbpalette(int colornum, int red, int green, int blue);
 

setrgbpalette can be used with the IBM 8514 and VGA drivers.
colornum defines the palette entry to be loaded, while red, green, and
blue define the component colors of the palette entry.
For the IBM 8514 display (and the VGA in 256K color mode), colornum is in
the range 0 to 255. For the remaining modes of the VGA, colornum is in
the range 0 to 15. Only the lower byte of red, green, or blue is used,
and out of each byte, only the 6 most significant bits are loaded in the
palette.
For compatibility with other IBM graphics adapters, the BGI driver
defines the first 16 palette entries of the IBM 8514 to the default
colors of the EGA/VGA. These values can be used as is, or they can be
changed using setrgbpalette.

/* setrgbpalette example */
 
#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
 
int main(void)
{
   /* select driver and mode that supports use of setrgbpalette */
   int gdriver = VGA, gmode = VGAHI, errorcode;
   struct palettetype pal;
   int i, ht, y, xmax;
 
   /* initialize graphics and local variables */
   initgraph(&gdriver, &gmode, "");
 
   /* read result of initialization */
   errorcode = graphresult();
   if (errorcode != grOk) {  /* an error occurred */
 
printf("Graphics error: %s\n", grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1);   /* terminate with an error code */
   }
 
   /* grab a copy of the palette */
   getpalette(&pal);
 
 
   /* create gray scale */
   for (i=0; i<pal.size; i++)
setrgbpalette(pal.colors[i], i*4, i*4, i*4);
 
   /* display the gray scale */
   ht = getmaxy() / 16;
   xmax = getmaxx();
   y = 0;
   for (i=0; i<pal.size; i++) {
 
setfillstyle(SOLID_FILL, i);
bar(0, y, xmax, y+ht);
y += ht;
   }
 
   /* clean up */
   getch();
   closegraph();
   return 0;
}

setpalette

  no output of example at the moment
  do not hesitate and add it...