private static Color CalculateColor(Color front, Color back, int alpha)
{
// solid color obtained as a result of alpha-blending
Color frontColor = Color.FromArgb(255, front);
Color backColor = Color.FromArgb(255, back);
float frontRed = frontColor.R;
float frontGreen = frontColor.G;
float frontBlue = frontColor.B;
float backRed = backColor.R;
float backGreen = backColor.G;
float backBlue = backColor.B;
float fRed = frontRed*alpha/255 + backRed*((float)(255-alpha)/255);
byte newRed = (byte)fRed;
float fGreen = frontGreen*alpha/255 + backGreen*((float)(255-alpha)/255);
byte newGreen = (byte)fGreen;
float fBlue = frontBlue*alpha/255 + backBlue*((float)(255-alpha)/255);
byte newBlue = (byte)fBlue;
return Color.FromArgb(newRed, newGreen, newBlue);
}