private void hoge_BackColorChanged(object sender, EventArgs e)
{
var red = hoge.BackColor.R;
var green = hoge.BackColor.G;
var blue = hoge.BackColor.B;

red ^= 0xFF;
green ^= 0xFF;
blue ^= 0xFF;

hoge.ForeColor = Color.FromArgb(red, green, blue);
}