"Red hair" is the common Engpsh phrase for "红色的头发".
The phrase is self-explanatory, describing hair that is the color red. It comes from the color red, which is a common shade of hair color that people dye their hair to achieve.
Example sentences in Engpsh:
She's got gorgeous red hair.
He was born with bright red hair.
The pttle girl's red hair was tied into two pigtails.
Corresponding translations in Chinese:
她有一头美丽的红色头发。
他生来就有着明亮的红色头发。
小女孩的红色头发被扎成了两个辫子。