A

Albus: What do you mean?

Scorpius: Don’t you ever get that small voice inside your head telling you something will get you in a lot of trouble?

Albus: No?

Lily Luna: *comes in and sits on the desk*

Albus: What do you want?

Lily Luna: Drive me to Taco Bell.

Albus: Why don't you drive yourself?

Lily Luna: We can talk shit about James.

I would like to expand on this theory: for generations now, any women married into the family would color their hair to match everyone else. However, they would refuse to tell anyone they were doing this artificially, except to explain this rule to the new wives as they got married in. From this came the theory that it happened naturally when you got married in. No one starts to figure it out until around Deathly Hallows, when Narcissa has not the time/resources to keep coloring it and the color fades into its natural black. Then, Draco marries Astoria and her hair never changes either.