In French, blond is masculine and blonde is feminine. This distinction generally extends to the English adjectives, especially in British English, where blonde is more common than blond (mainly because the word is used in reference to females more often than than to males). In American and Canadian English, blond is generally preferred over blonde in all cases—even in reference to female hair color—though a minority of writers continue to observe the gender distinction. In any case, using blonde in reference to male hair is simply a misspelling.
The use of blonde as a noun in reference to a female with blonde hair is best avoided because it can be interpreted as sexist.
These British publications take gender into account when using blonde and blond:
The blonde bombshell struck one sultry pose after another which perfectly highlighted her long tanned limbs. [Daily Mail]
He should be delighted with his smooth complexion, twinkling blue eyes and thick blond hair. [Express]
Tonight we learn that she’s definitely blonde and a lady. [Guardian]
Although some American and Canadian writers consider gender with blonde and blond, most use blond for all purposes—for example:
Their sister, Gutrune, with long blond hair, seductively lounges on a sofa, bored with their ruler-of-the-universe ways. [Los Angeles Times]
Now, Greenpeace is accusing the curvy blond doll of having a “nasty deforestation habit.”. [Globe and Mail]