During the early years of the Internet, there were 216 web-safe colors that standard PC VGA monitors could display in 8-bit mode. A more important reason for flat color use during those years was because flat graphics compressed to smaller sizes during a time when transfer speeds were a tiny fraction of what they are today.
However, I doubt any flat-color web design trends are rooted in those limitations. Flat colors have been around since caveman days. There are deliberately retro reincarnations rooted in the styles and technical processes of the 1980s, '60s, '50s, etc. Still, I think the main reason flat colors are sometimes used for interface designs is because they’re simple, they look good, and they were (and still are) refreshingly different from the skeuomorphic look that preceded them.
I pay attention to trends, but I don’t look to them for inspiration in my work. I think trends appear for two primary reasons: 1. Designers notice a look they like (such as flat colors) and then incorporate that look into their work. 2. Technical advances create new possibilities for doing things differently.
These changes aren’t trends until people begin noticing others doing the same thing, which is often a good time to jump off the bandwagon as the trend followers are jumping on.
What I find objectionable is the trend of designers thinking trendiness is something to incorporate into their work, as if it’s essential for some reason or another. Some (misguided) design college instructors seem to promote the idea. Design bloggers and podcasters who constantly need to invent something to write and discuss have made trend prediction and analysis a staple of their work.
In this flurry of less-than-important information about trends, design students and new designers, who soak up new information like a sponge, take for granted that everything they learned in school and heard on a popular podcast is important.
I’m a big proponent of higher education for graphic designers, and I went that route myself for both a BFA and an MFA. However, much of what I learned in school needed to be painfully unlearned or modified once I graduated.
Clients and employers rarely, if ever, concern themselves with trends. To them, the reason they hire designers is because business needs warrant them. More often than not, that need is very much goal-oriented — improve branding, improve sales, improve traffic, improve shelf appeal, make more money, improve their Net Promotor Score (another unfortunate trend), etc.
Once former design students finally make the often difficult transition from design students to design professionals, they typically realize that using their talents to solve client and employer business problems is the primary goal. Doing this rarely involves latching onto here-today, gone-tomorrow trends. It’s certainly inappropriate to use a client’s or employer’s business problem as an excuse to incorporate one’s own aesthetic preferences and desire to be trendy, which, more than likely, aren’t the most effective solutions to the problem at hand.