I live on a small wetland lake on the border of Auburn Hills in Michigan. Each year we have a pair of Mute swans give birth. Last year was the only year one cygnet survived. Out of seven born this year, three have survived. Two are white and one is dark gray. It appears to get darker as it grows. It has a black bill, while the other two have bills beginning to turn orange. Is this common? Will the dark one eventually turn white?