I love this addon WHEN it doesn't correct my British English spellings into American ones. I've read your instruction - there is no English "(no variant)" in settings, and selecting "British English" in "Interpret English as:" doesn't stop the addon from correcting my British spellings. This has to be a bug.
I have just tried with "colour" and it gets accepted when British English is selected. Please contact our support at support -at- languagetoolplus.com with a screenshot of your settings and a screenshot of the text.
