My mother, who was Canadian, had a saying that you could not wear white after Labour Day. Of course this made no sense to me whatsoever as a kid in England. We didn’t even have Labour Day!
Here in Canada it makes a little more sense when you see how this public holiday is used to mark the end of summer. Schools go back immediately after Labour Day. People are on their way back from their vacations, stocking up on school supplies and shopping at all the back to school sales.
I don’t know if rules about what you wear were stricter in my mother’s day, but I doubt that the social faux pas of wearing white in September would have made much sense even in those days!
For my part I intend wearing shorts and summer shirts for as long as the weather allows. I might even go into full Canadian gear and don a fleece, big boots and keep the shorts. My socks may be white, but the rest of my stylish outfit will be season appropriate.