Ahh! The beautiful world we live in full of color. Color comes from light and how it reflects off surfaces, be it paper or a computer screen. Color permeates many aspects of our lives, from what we decide to wear in the morning, to the furniture in our living room, to the paint on our walls, to the flowers we decide for our garden. As inferred, just as color has a place in our everyday lives, it has a definite role to play in graphic design. It can affect how a logo, brand, website, and/or a marketing campaign is perceived. It represents a mood, a perspective, even a message, depending on how it's applied and with what combination of colors. Hence the importance of learning basic color theory, so you can apply color principles to your design projects.
Warm and Cool Colors
In order to understand complementary colors, we need to know about primary colors and secondary colors. Primary colors are red, yellow and blue. Secondary colors are orange, green and purple and are created by blending two primary colors. Complementary colors is the combination of a primary color and its counterpart — the secondary color located on the opposite side of the color wheel. Examples in the color wheel above illustrate the following complementary combinations: red and green, blue and orange and purple and yellow. As the name implies, "complementary colors" go very well together and can be a simple, yet efficient guide as to which combinations to use in layouts.
The Itten Star
Below are two useful links about the Itten Star. The first link shows visual images of contrast combinations formed on the basis of the Itten Star; while the second link is a nice website about Johannes Itten — his life and his contribution to color theory and design.
Again and again, I reiterate the same principle, in that, it is the design project and its overall message which will be the driving force and ultimate guide in determining how to apply the design principle at hand. In this case, it is what colors to use which will enhance and express your design project's message most effectively!
I hope you've enjoyed these short, but informative morsels about graphic design principles. More to come over time!