I've seen speculation that the trend towards monotony and less flamboyance was more due to the widespread involvement of men in the military for the first half of the 20th century.

I also read somewhere that, before the revolution in France, the nobility dressed very colorfully and flamboyantly, but the lower classes were required to wear plain drab clothes. After the revolution, during the terror, it was very dangerous to wear colorful or elaborate clothes - if anyone got the idea you were of the nobility, you were dead. So everyone dressed drably. Supposedly the practice caught on all over Europe, because even then France set the fashion; and the habit stuck with men, but not women.

Peter.