Since the beginning of what anyone would call the formal study of logo design the masters have extolled the virtues of the 1 Color design. Like many arguments of a qualitative nature, this used to be frequently reduced to some financial or technical (in other words, quantitative) argument in order to convince the non-believers acquiesce. In the age of mimeograph and fax machines and four color process printing that required the creation of multiple physical printing plates, often by hand, it was easy to argue that having a logo that worked in 1-Color was the only fiscally responsible course of action. However, in the age of the web-only company and four color process printing that often costs less than 2 color (or even 1 color for metallics) spot printing, and with the significantly decreased relevance of the fax machine, it's easy to think,

"Well, we can have logos that only work in full color now! Right?"

Wrong.

The Only Medium That Matters: Your Brain

As it turns out, the simple logo has a distinct advantage in the one place that matters. You see, for any production or output method for any logo in any application, there is a single point of entry to your potential customer's decision making (and a single point of failure for your logo): Their Brain.

Alina Wheeler expresses this pretty deftly in her book Designing Brand Identity. Your brain processes stimuli by breaking down tasks and processing them in order. For a logo this means that your brain first recognizes the shape of something, then the color, then the content. Since the point of logo design is differentiation, this has a few implications:

1. A unique shape will serve you better than a standard one - Simply put, if your brain recognizes the shape before anything else, why would you want it to be the same shape as 100,000 other spheroid logos?
2. Fewer colors means less to process - Why clutter up the cognitive queue with a list of colors to process? Does your logo need to be green and blue and orange and pink? Could you make the same point with fewer colors? You'll speed up recognition, and you'll get to the part where the viewer interprets the actual content of your logo much faster.
3. Less "Stuff" is better - The last step is the one where they read your name, or see your symbol, or interpret your mnemonic. Keep it brief. By the time we get to this point in the process our fraction of a second is almost up. Make it easy for them to come away with any reason to remember your logo.

Your Brain is a Simpleton

So there you have it. The ultimate reason that a simple logo is the best logo: our brains. No matter what technological improvements we make, we'll still be processing the stimuli as a simple shape first. In a few years we'll all be watching holographic 3D TVs in our homes and being barraged by animated, computer generated, ray-traced logos, and the ones that work the best will still be the logos that keep it simple. We can't change the way we perceive these things anymore than any other subconscious process, so if you're a designer, use this knowledge to your advantage, and if you're looking for a logo designer, well, you know where to find me.