Given the importance of accessibility and usability in the creation of successful applications and sites, I’m always really, really surprised at how little attention is given to color.

There’s no shortage of psychological and scientific studies proving that actual physiological changes take place in human beings when exposed to certain colors. Colors can stimulate, excite, depress and tranquilize. They can affect appetite and physical perception of temperature. For those among you who share my geeky fascination with such things, this is known as chromodynamics.

In the world of UX, the psychology of color is one of the most powerful tools in a designer’s arsenal. The color decisions you make in designing an interface directly influence how your product makes the user feel – upon the very first glance at the screen.

In my own experience in usability testing labs, color can often be the critical factor that determines the user’s level of comfort in interacting with what’s onscreen. Poor color choices equal poor user experiences. At best, a person feels calm and comfortable, finding it enjoyable to move through the application at his own pace. At worst, harsh colors and combinations involuntarily pull the user’s eye away from the areas she needs to see or interact with – so she feels tense or anxious, and possibly like she’s unable to use the product.

So how do we, as UX professionals, producers and designers, make informed color choices? Which colors fire people up? Which ones convey a sense of dependability? How can we apply the psychology of color in our design work?

Explaining all of this in detail would most likely surpass all of our ever-shortening attention spans (thanks, TiVo). So instead, with a little help from our friends at the Pantone Color Institute, here’s a quick primer on some basic colors and their meanings.

Red is probably the most widely-studied color. Our fascination with red stems from its natural connotations of excitement and danger, fire and bloodshed. We pay attention to red because it can evoke a psychological fight-or-flight response; blood pressure rises and the system is flooded with adrenaline; the heart beats faster. The color is a warning signal that has been imprinted, repeated and reinforced for generations. In addition, red is the color with the most energy. The physical stimulation associated with red means that it often carries a sexual connotation (Red Light District). Red is often a favorite choice for designs relating to alcoholic beverages and racy cosmetic or fashion lines.

Blue is the absolute antithesis of red. We associate blue with feelings of serenity and tranquility. Blue conjures up relations of sky and water. We relate blue with dependability and consistency – which explains why corporate branding often uses blue in order to communicate reliability.

When we see green, we see nature; the ideas of freshness and cleansing come to mind almost immediately. Research shows that consumers often cite blue and green as their favorite colors; color experts attribute this to the fresh and calm feelings associated with these colors. Green does a good job of projecting healthiness and freshness, most notably in packaging or collateral.

In a large number of cultures, yellow represents the sun. Lighter yellows inspire a more cheerful and inviting feeling, while brighter yellows get our attention quickly. Bright yellow is the most visible color in the spectrum, especially when paired with cool colors – think blue and green – that retreat in our field of vision. Yellow evokes culturally universal feelings of enthusiasm and positivity.

As a combination of red and yellow, it’s only natural the orange would inherit the qualities of both colors. Orange can encompass the dynamic excitement of red as well as the warmth and good cheer of yellow. From brilliant neon to a soft, rich terra cotta, orange has a wide spectrum of hues. Orange’s energy is often associated with festivity and celebration, making it a popular color with children.

Historically, black has been associated with grief, considered funereal. But these days black is all about being upscale, evoking power, elegance and sophistication. Black is an excellent choice for marketing an elite product, service or organization, particularly among urban audiences.

A blend of red and blue, purple is the most complex color in the spectrum. When the shade leans toward red, it gets hot and sensuousness in the hue is brought out. Blue tones cool it down, making these variations of purple more sedate and calming. Purple has long been associated with royalty, because at one time the dyes used to make it were extremely expensive to make; only the very wealthy could afford purple clothing. The UK’s Cadbury chocolate, for example, has used purple packaging for years to associate a sense of royalty with its chocolates. Purple can be a good choice when targeting more creative types; the color sparks excitement and grabs consumers’ attention.

Associations with brown can be both positive and negative – earth or dirt, depending on your perspective. That said, the perception of brown has changed over the last several years. Now commonly associated with coffee (Starbucks anyone?) and chocolate, brown enjoys an air of deliciousness. Through association with rich fur and dark wood, brown also suggests luxurious qualities. At the same time, lighter and more neutral shades of brown evoke a sense of wholesomeness and honesty in their down-to-earth overtones.