ImageEnView1.IEBitmap.Palette[AIndex] := TColor2TRGB(clGreen);
    ImageEnView1.Update;

procedure ChangePalette;
var
  LogPal: TLogPalette;
  hPal: HPalette;
  PalEntry: array[0..255] of TPaletteEntry;
  i: Integer;
begin

  for i := 0 to 235 do 
  begin
    PalEntry[i].peRed := i;        
	PalEntry[i].peGreen := i;
    PalEntry[i].peBlue := i;
    PalEntry[i].peFlags := PC_NOCOLLAPSE;
  end;
  
  LogPal.palVersion := $300;
  LogPal.palNumEntries := 1;

  
  hPal := CreatePalette(LogPal);
  ResizePalette(hPal, 256);
  SetPaletteEntries(hPal, 0, 256, PalEntry);

  
  SelectPalette(ImageEnView1.IEBitmap.Canvas.Handle, hPal, FALSE);
 
  RealizePalette(ImageEnView1.IEBitmap.Canvas.Handle);
end;

procedure changePalette;
  pal: array[0..255] of TPALETTEENTRY;
begin
  pal[2].peRed   := 255;
  pal[2].peGreen := 100;
  pal[2].peBlue  := 0;
  pal[2].peFlags := 0;
  SetPaletteEntries(ImageEnView1.Bitmap.Palette, 2, 255, pal);
end;