Can I dye my hair blonde for a day?

Not exactly... the term "dye" causes a lot of confusion, but dye generally means making the hair darker. To make the hair lighter you must use a special bleach. Hair bleaching is permanent and cannot be rinsed away. It can be dyed back to it's original color however, but the bleach does damage to the hair. In extreme cases, where the hair was dark brown or black and is bleached to blonde, the hair becomes very thin and resembles the texture of cotton. You can lighten hair temporarily by using theatrical hairsprays. These come in every color of the rainbow including white, gray and blonde. These color sprays actually sit on the outside of the hair strand, and can be shampooed completely out after brushing the hair.