The choice of color in graphic and web design is not arbitrary — characteristics of color, whether visual or cultural, are very important when determining hierarchy and anticipating the user experience.
How the human eye sees color — in a nutshell
Objects in the world absorb or reflect light. Our eyes contain tiny photoreceptor cells in the retina called cones which respond to that light. The wavelength in the light spectrum (red, orange, yellow, green, etc.) that is reflected determines what color we see.
Blue is generally less sharp to our eyes
We have less of the blue cone photoreceptors in our eyes which means we are not very sensitive to blue light. This makes blues generally less sharp or crisp. On the otherhand, we are very sensitive to red and green light because we have more red and green cones in our eyes. As we age, blue becomes even more problematic. Something like light blue text on a blue background may have very poor visibility to an elderly person.
Grab attention with contrast
The attention-grabbing factor when using color is the contrast it has in context to its environment. Luminosity, or brightness of that color, can help to increase contrast. The brighter something is against its environment, the more it will stand out. High contrast items travel to our brain the quickest, winning our attention and retention.Our eyes have the highest sensitivity towards bright yellow on the visible light spectrum making it a highly visible, attention-grabbing color. Yet, yellow is a tricky color to work with in design because it is so bright. Contrast needs to be carefully taken into consideration in order to grab the most attention — think bright yellow text on a white background vs. a black background.
Colors are always less vibrant printed versus on screen
Colors viewed on screen are brighter than when printed because of the emitted light from the screen. Brightness is toned down when printed. This is something that should be considered in print design — the colors and contrast of what you've been seeing on screen during the design process will certainly look different when printed and absorbed on physical paper. Because of this it's very important that you chose a printing method and paper that will give you your intended result.
Cultural experiences
Another consideration when working with color is to understand the culture of your audience. Colors can have very different emotional attributions and mood reactions in different cultures. Designing a website for a population in China versus the state of Florida may result in very different color decisions as a designer. To a Florida audience, the color orange will most likely remind them of the state fruit, but in China it may signal spontaneity or change. It's very important to know your audience and make informed color decisions in design.