While color usage isn't an exact science, it can definitely influence the outcome of a direct mail campaign. According to Cynthia Cornell, Color Researcher with Color Communications Inc., "Always be mindful of the message you want to convey and how you want customers to perceive your products."
Color Communications Inc. provides the following list regarding hues:
Blue-based reds are associated with more expensive products. Select a yellow-based red (like tomato red, which is perceived as less expensive) if you're looking to downplay a high price.
Orange plays up affordability. Green conveys possibility and hope.
Yellow is the first color the eye sees, and when used with dark colors for high contrast, it becomes more powerful and easily read.
Blue portrays confidence and safety, which is why it's such a popular choice for financial and medical institution mailers.
Purple, although especially hot right now, is best used with high-fashion or sweet treats rather than direct marketing.
Black conveys a strong sense of power, promise and the ability for high contrasts. Add sheen or matte to black, and it becomes more powerful still.
White (especially when presented tone on tone) implies sophistication and formality -- but also a high-end price point.