The spelling of the word color as "colour" means your button was made in Britain. The 1-piece flat brass buttons with an "incised" backmark (instead of a raised-letters backmark) date from approximately 1810 to the early 1840s. Being plain-faced, after that time-period they fell out of favor with the public due to the advent of button-making machinery which could inexpensively produce 2-piece "ornate" buttons.