I'm Spanish and I'm full-blooded white. Many times I've been called Hspanic just cause I'm a Spaniard.
Yes, Spanish is a white language, as last time I checked, Castillian (or Spanish) was the language of Castile, now Spain, which is in Europe. Yes, the reason people of all these races speak Spanish is ecause of the Spanish empire and the colonisation movement.
I think, the reason that most people think Spanish is not a white language is because of the large population of Spanish speaking non-whites (and ignorance), like you said. Since latinos of mixed race greatly outnumber Spaniards, people go with the majority. Just like stereotypes. As for Spaniards having Arab blood, yes, that is true in most cases, since the Moors (Arabs) conquered and ruled most of the Iberian peninsula, for like, a millenia. But wait, I said Iberian peninsla-not just Spain. Meaning: Portuguese people may also have Arab blood. Yet, no one says Portuguese isn't a white language, because there are not as many non-white Portuguese speakers than white.
However, what's funny as that they don't think the same of English. English is spoken by many non-whites and still considered a "white language", quite unfair if you ask me.
I'm Spanish and I'm pretty pale-skin colour has nothing to do with race.
It's not that people don't care about world history, it's just that most (but not all, let's not make fun of our educated friends) are ignorant of it.
I'm a Spaniard, baby~ xD