C / C++ / MFC

//! Retrieves an appropriate text (foreground) color for a specific
//! background color.
//! @param  rgbBkgColor Background color.
//! @return Foreground color.
COLORREF CDlgWeatherMate::getTextColor
  (COLORREF rgbBkgColor)
{
  COLORREF rgbText = RGB (255, 255, 255);
  int nRed = GetRValue (rgbBkgColor);
  int nGreen = GetGValue (rgbBkgColor);
  int nBlue = GetBValue (rgbBkgColor);
 
  int nBrightness = (nRed*299 + nGreen*587 + nBlue*114) / 1000;
  if (nBrightness > 150)
     rgbText = RGB (0, 0, 0);
 
  // Exception(s)
  if (rgbText == RGB (255, 255, 255)) {
      if ((nRed == 0) && (nBlue == 0) && (nGreen > 153))
         rgbText = RGB (0, 0, 0);
  }
 
  return (rgbText);
}

/// Determines the luminosity of a color
/// @param color Color to determine the luminosity of
/// @return A number indicating the luminosity of the color
int AfxGetLuminosity(COLORREF color)
{
	//------Last Checked------//
	// - June 13, 2003

	// Constants
	const int HLSMAX = 240;
	const int RGBMAX = 255;
	
	// Get the individual color values
	int nRed = GetRValue(color);
	int nGreen = GetGValue(color);
	int nBlue = GetBValue(color);

	// Get the maximum and minimum value of the colors
	int nRGBMax = max(max(nRed, nGreen), nBlue);
	int nRGBMin = min(min(nRed, nGreen), nBlue);

	// Use the "magic" formula
	return (((nRGBMax + nRGBMin) * HLSMAX) + RGBMAX) / (2 * RGBMAX);
}

...

COLORREF colorText = ((AfxGetLuminosity(colorBackground) > 120) ? RGB(0,0,0) : RGB(255,255,255));

strcpy (cText, "The number is: ");