SpellCheck Highlighting American English as Incorrect

Every time I type a word such as "Color", "Flavor", etc, it always highlights it as incorrectly spelled, trying to get me to type it in British as "Colour" or "Flavour". Oddly, this very page is currently highlighting the British version as incorrect, trying to get me to type them in American.
Both versions should be considered correct. This only started in the last week or two after some update.