public static Color ShiftColor(Color c, int shiftAmount)
{
int newRed = c.R;
int newGreen = c.G;
int newBlue = c.B;
// Red to purple
if (c.R == 255 && c.B < 255 && c.G == 0)
newBlue = newBlue + shiftAmount;
// Purple to blue
else if (c.B == 255 && c.R > 0)
newRed = newRed - shiftAmount;
// Blue to light-blue
else if (c.B == 255 && c.G < 255)
newGreen = newGreen + shiftAmount;
// Light-blue to green
else if (c.G == 255 && c.B > 0)
newBlue = newBlue - shiftAmount;
// Green to yellow
else if (c.G == 255 && c.R < 255)
newRed = newRed + shiftAmount;
// Yellow to red
else if (c.R == 255 && c.G > 0)
newGreen = newGreen - shiftAmount;
newRed = BringIntInColorRange(newRed);
newGreen = BringIntInColorRange(newGreen);
newBlue = BringIntInColorRange(newBlue);
return Color.FromArgb(c.A, newRed, newGreen, newBlue);
}