La Sueca, I, for one, am not offended. It is just that it itches a little when many times you are identified abroad with the dark skinned black-eyed black-haired 'torero' when u r not, and maybe I (we) are a little sensitive on that. But your question is reasonable.
Besides, along with the 4.000.000 spaniards living in Madrid, there are about 1.000.000 latino ans morocchian inmigrnats, and most of these ARE impressed by blondes.
I personally feel that being impressed by blondes is proper of underdeveloped societies. It probably has nothing to do, but that's how I understand it, after, e.g., being told once by a Cuban girl that all her brothers and sisters had "improved" or "gone forward" because they married whiter or blonder couples. She actually said that, because she was pretty extroverted, but it's not difficult to see if you speak with latinos, or africans (at least) that this idea lies in their culture.
I have been about 10 days in Poland and about 15 to 20 people ask me an adress while I was there, guess what, they all thought I was polish, haha.
Here, in Czeck Republic, have only been asked twice in Czeck, but I have only been here for 4 days now, :p
Fair blondes in spain, let's say straw-like colour are very very very unusual, and when you see one spanish, it's thanks to chemical products 99% of the times.
As for canary bird-like yellow, this is pretty uncommon, although you'll see more (apply here the chemical rule in a 90-95%) Other darker blonde or fair hairs are more and much more common respectively.
As for Quintos, I think he means by "dirty blonde" a darker blonde colour (language imperfections, eh Quintos?)...