I wonder how often these discussions crop up where people complain about the form of dialects/accents/whatever-you-wanna-call-them that developed in places removed from the language's origin in other languages? Like, do Spain-Spanish speakers dislike Mexican-Spanish? If so, is it from a perceived 'bastardization' of their language like the worst of the non-American English speakers feel about American-English? Or is it more like the, "Why do they spell it that way when it was already spelled this way?" Or maybe even just, "We are ostensibly speaking the same language, but I can't fully understand what they are saying! I am enraged/offended/discouraged!"
Honestly, considering that the US broke away violently, what surprise is there in some aspects of the language being altered?
The truth of the matter is that silly differences like "colour vs color" shouldn't illicit such a strong reaction in people because the language branched slightly at that point; so those saying colour is correct and those saying color is correct are both right and wrong to precisely equal degrees. Colour is the current spelling from the language's origin and color is the form used in a place that isn't the origin. This really shouldn't surprise people beyond the point where they understand that's how somewhere else spells/uses the word and after that any anger/distaste is just being either elitist in the former's case and boorish in the latter's.
Also, as for the little red line issue, that should be from your browser's dictionary rather than the site's text box. At the very least Google Chrome is using a dictionary from within the browser as "Sarest" isn't underlined for me after I added it to the dictionary on another site.