There’s an old story which isn’t true, but should be:
In 1837 the commander of the H.M.S. Blazer, a frigate in Her Majesty’s employ, caught wind that a young Queen Victoria would soon be inspecting his charge and, intent on impressing Her Majesty, replaced his crew’s usual decrepit togs with short blue jackets. The jackets were fitted out with Royal Navy brass buttons and, in some versions, the jackets were striped in navy and white also. In others, there are no white stripes. Regardless, the young Queen was so taken with the jackets that she required them of all men sailing under her colors, ever after.
Another, equally unverified story is that 19th century Brits took to emblazoning their blue jackets with the crests and decorations of clubs, schools, and military units.
In either event, the blazer was born and it was blue and had brass buttons. In fact, the blazer is the only men’s jacket which is allowed brass buttons. All others take horn, leather, shell, or plastic.
Scrubbed down, the moral is this: blazers are blue (with few exceptions, notably the green blazers worn by alumni of Dartmouth College and some very good golfers) and they come with brass buttons. Jackets which are patterned, textured, or fitted with buttons made of anything but brass aren’t blazers; they’re sport coats. The difference is a matter of arcane minutiae, true, but it’s the type of thing by which the wheat is seperated from the chaff, and the initiates from novices. And anyway, if you’re going to wear clothes, you ought to know what they are.