Perhaps you meant:
* Double process hair color: This is a technique where hair is lightened (bleached) and then toned with a second color.
* Double-toned hair: This refers to hair that has two distinct colors, often achieved with highlights or balayage.
* A specific brand or product name: If you're thinking of a particular hair dye or treatment, please provide the full name.
Let me know if you can clarify what you meant by "Double hair," and I'll do my best to help!