How do the Pros determine which trends will fade and which ones will rise?

The “pros” don’t predict the trends, they create the trends. They choose what to do based on past popular trends and the cultural climate at the time, as well as paying attention to the trends in other markets, particularly those in Europe and Asia, as well as popular trends music, movies, television, celebrities, etc. For example, when Walk the Line premiered, there was a slight resurgence in fashions similar to those trends. Consumer reports, surveys, and sales records are good indicators of where things are going too.

I don’t feel like my tastes are very much, if at all dependent on the ‘determined colors (or styles),’ though am often surprised at they are concordant with certain designers’ interests.

I guess think there is, at times, a sort of collective unconscious behind this. Though, in the a post-modern era like today, anything or combination or motifs can be cool to some group of people at any given time.

Perhaps the people you mention are just really good at detecting these trends, though they might take credit for determining them.

Trend creators don’t always get it right. As an example, GAP’s season of “Boyfriend Pants” pretty much caused sales to tank that year, and they have yet to recover.

I think there’s a trickle down effect from designers.
But designers also ultimately get inspired by consumers themselves.
There seems to be a growing interest in what “normal people” are doing.

In the past, designers have gotten inspired by traveling and seeing what the youth in the streets were wearing. Scandinavia, Japan, etc. With the internet boom, blogs are crafting their own kind of trend-setting culture.

Blogs like The Satorialist give readers a glimpse of the international street.
People aren’t just riffing off of Jane down the street anymore.

Even sites traditionally used for straight up commerce like Ebay are cultivating their own culture of image. Everything’s already been done. People looking for the new are sifting through the old…ready to put their own personal twist to it.

Between the two (what people* are wearing and what people are buying),
you can generally predict what you will see on the runway next season.
* The word trendsetter is so retarded. But basically people who are rabid design consumers.

And based off of what you see on the runway this season,
you can generally predict what you will see in the stores in a year or so.
(But a much more watered down, marketable version.)

I’d say the same goes for interior design as well.
Before you couldn’t really get a glimpse at what “normal people” were doing.
But now interior design and home blogs are popping up everywhere.

But I’d also have to agree with Peedub.
There does seem to be some collective independent consensus.
The phenomenon is rather peculiar.

There are professional “cool-hunters,” who play a significant role in identifying trends. Malcolm Gladwell wrote about it in the New Yorker back in 1997. There’s also a website about cool-hunting. And, of course, there’s the Wikipedia definition:

Coolhunting is a term coined in the early 1990s referring to a new breed of marketing professionals, called coolhunters. It is their job to make observations and predictions in changes of new or existing cultural trends. The word derives from the aesthetic of “cool”.

There are cool-hunting firms, undercover cool-hunters, and even open source cool-hunting. The latter provides free information about trends from this website.

I would say there’s a reciprocal relationship between designers and the cutting edge public. Sure, companies push what they decide will be the current trend, and the public, to some extent, has to buy it, if they want to have new clothes and accessories. However, the designers are also always researching emerging trends that they can then sell to the public.

haha @ the devil wears prada reference, i was definitely thinking about it reading the question.
i don’t really know, i was wondering the same thing myself.
i think – in ‘style’ – a lot of times one designer kind of does something and the others start to follow and naturally it trickles down to Forever 21 where it explodes and eventually ends up being a victim of overkill.
but in a lot of cases, it starts on ‘the streets’. in other words, just normal people – and sometimes bands – start something, and it inspires designers.