This is another aberration of the 90s that continues to wreak havoc on the faces of those who were teenagers and twenty-somethings in the period when hair dye and sideburns were definitive markers of some sort of subcultural or "alternative" affiliation. At the time, I think, it communicated a general disaffection with normativity without a clear affiliation to anything in particular, excepting enjoyment of the recorded music of Nirvana.
The hideousness of this combination reaches an apex when dudes with dark facial hair choose to maintain their chin-strap or sideburns despite lightning their non-beard hair. Don't do this it makes you look like you have mange! Don't grow facial hair if you plan on bleaching or dying your hair in a shade that is significantly different from the color of your facial hair!