THIS year marks the centenary of the birth of Marilyn Monroe, and is being celebrated by the British Film Institute and the National Portrait Gallery. The BFI is showing a two-month season of her films, while the National Portrait Gallery charts the construction of her image.For much of the mainstream media and even among the general public, Monroe was seen as the epitome of the “dumb, beautiful blonde” and an icon of the silver screen. She was, however, not a natural blonde and certainly far from dumb.