Many years back I used to practice social skills and pickup. I realised quite quickly while learning how to socialise that colour is one of the more important ways to alter how others perceive you prior to knowing you.
Specifically, greys and blacks were generally a bad choice and tended to signal low-confidence or a lack of character. There is an exception here for formal wear, but generic fashion choices like a black tshirt, grey shorts and black shoes will make you look devoid of personality. Always try to wear some colour if dressing casually and if you want to appear more friendly soft blues, greens and pinks I think are some of the most inviting colours.
Hot pink was one of my favourite colours to cautiously add when socialising as a guy in a casual setting because it can be quite an interesting colour choice. It's far less aggressive than a strong red, but almost equally as striking. And its purpose is more confusing (and therefore interesting) than other colours since it could both be a sign of a confident heterosexual guy, or an outwardly gay guy. For this reason I've found hot pink is a good colour to add if meeting girls in a casual setting because it can be initially sexually neutralising while also an indicator of confidence (being too sexually forward is generally a bad strategy).
However, in a formal settings whites and blacks are generally what you'll want to go with. Beige colours can also work, but might make you look a bit old fashioned today. I thought the reaction Jordan Peterson got when he starting wearing very colourful and striking suits was interesting because it confirmed a lot of my speculation around how people view colour in formal wear. It's very, very difficult to balance class with colour. If you want to appear classy it's almost required that you stick with whites and blacks.
I personally suspect the world is losing colour because of the above two points – we associate class with neutral colours (blacks and whites generally) and strong colours can impose strong emotional responses which we might want to avoid (generally speaking anyway).
My guess is that if you saw a brightly coloured home or car you will have a sense that the person who owns that thing has a lack of class and a strong colour might even suggest something negative or unintended about the owner. For this reason you might be tempted to just stick with something neutral to avoid this. This would be especially true for colourful items of low value because creating a strong emotional reaction around an item of little value it's probably going be perceived as overwhelmingly negative. Hence why some teen driving fast in a bright red but inexpensive car can be aggravating, while someone else driving fast in a bright red Ferrari while not especially classy is still likely to be far less negatively perceived.
And beyond the class aspect, I'd suspect the lack of colour we see today is a reflection of our lower self-confidence both as individuals and culturally. I suspect people increasingly don't want to stand out or make an impression in public, and culturally in the West we're less confident and perhaps don't believe our public buildings deserve to be as striking or grand as they were in the past.
I don't really know why blacks and whites suggest class either. I suspect that's a cultural thing that could change, but perhaps that would first require us to be confident enough to make an emotional impression. Perhaps too much confidence is viewed as unclassy today, while being timid and softly spoken is generally seen more positively. Either way, even if you believe the world should be more colourful, I wouldn't suggest leading the way on that in your own life – at least not if you care about how others will perceive you.