In terms of hair color:
* Brunette: This is the most common and direct opposite.
* Redhead: Red hair is distinct from both blond and brunette.
* Black: This is another common opposite, although many people have hair that falls somewhere between black and brunette.
* Dark: This is a general term encompassing all shades of brown, black, and red.
Beyond hair color:
* Dark: This could also be used to refer to the opposite of blond in other contexts, like a blond wood versus a dark wood.
* Light: This is the opposite of dark in many contexts, and could be considered the opposite of blond in a general sense.
So, the best answer depends on the specific context!