As Smokey already mentioned, the spelling of color as colour in the backmark means British manufacture. We know that the presence of indented lettering in a brass 1-piece flatbutton's backmark dates it to being made sometime between about 1810 and the late-1830s, which was pretty much the end of the 1-piece flatbutton's era. Also, Americans were boycotting British-made goods for about a decade after the end of the War-of-1812 (ended in 1815). So, the odds favor your British-made flatbutton arriving in the US sometime between about 1825 and the very-early 1830s.
Thanks for the replies. I’m really excited it is so old, considering I found it in Saskatchewan, just up from North Dakota. I’ve never found a flat button like that around here before. Maybe this new spot I’m hunting has some great potential.