I don't know if red prior to 1940 was a gendered color. There is that famous quote about how pink is a strong color and therefore for boys and blue is more "dainty" and feminine. But that was like one magazine, there were others that said blue was better for boys etc. There was no real culturally defined gender seperation.
I think the main shift just came with people 1. being able to buy a ton of commercial toys for their kids during the economic upswing making some marketing strategy important (see also how video games became associated exclusively with boys, same thing a few decades later) and 2. parents preparing for a specific gender because you could now know that months prior to birth
In western culture color has always been more closely related to class than gender imo - there were actual laws regulating what colors you are allowed to wear depending on social status. I know of no colors regulated or seperated by gender until recently. I'd argue the true red vs blue divide is the "blue blooded" higher classes vs the red (socialist) workers. That's why the right wing party in most countries (america excluded) is blue and the left wing parties are red. >>66642
High heels were used for horse riding, then men used them for fashion purposes (famous example pic related, louis the 14th). If you think about it there are still shoes that have raised heels like cowboy boots.