Depending on the context, either “blond” or “blonde” can be the proper grammatical choice in a sentence. The rules for this are pretty simple. Because the word blond(e) is French in origin, it comes in two different ‘genders’: masculine and feminine. This rule holds true for English also, so when you are referring to a light-haired male you use blond, and when you mention a light-haired female you use blonde. The only other thing to remember is that there is only one spelling when the word is used as an adjective: blond.