Lippe is a girl.
Before she's using magic to change her hair color to blonde so Bliss don't feel insecure. Her true hair color is the same as Ash.
And she wear pants because she doesn't want other nobles to criticise the royalties for not having a boy to succeed the throne. So Lippe maintained her hair short and wore pants to satisfied the nobles.
That's what i understand base on Lippe's story about the future.