I started as a natural blond, but over the years my hair got darker. For a long time I had, according to the hairdresser, a combo of dark and ash blond hair. Nowadays most people would describe me as a light brunette.
I haven't colored my hair very often, but when I did it wasn't blond. As of course you need to bleach and or decolor the hair to be able to color it blond. The only thing blond would be my short lived coup soleil (some blonde streaks in my hair) in my early 20s. Otherwise I most of the time ended up with reddish colors, for which no bleaching or decoloring was needed.
It is easy to understand that bleaching and/or decoloring of the hair can have a negative effect on the hair itself. Even when it is done by a well experienced and great hairdresser.