The first impression you make on a potential employer is the most important one. Within the first 10 seconds, the first judgment an interviewer makes is going to be based on how you look and what you are wearing. In some more conservative environments, appearances do matter. In other environments it may not be as important. However, it does make sense to dress your best for the interview, regardless of the dress code at the organization.
The most important thing you bring to an interview is confidence. What you wear and how you wear it helps convey that. If you aren’t comfortable, that will come across in an interview.
You want to wear colors that show you will fit in with the company's culture. In an office that tends to dress more conservatively, you should definitely stick to neutral, solid colors. However, in more casual offices, such as some startups and nonprofit organizations, you can feel comfortable wearing a bit more color. Wearing solid colors helps ensure that your clothes will not distract. Solid navy, dark gray and black suits and dresses in particular look professional without being distracting. You’re definitely welcome to add a pop of color to a neutral interview outfit.
The color of your clothing sends a subconscious message to the interviewer about your personality. Softer colors in particular work well for more casual offices, because they convey a bit of personality without being overwhelming. Pale colors are a great way to add color without appearing too authoritative, and are great for people-friendly jobs such as service positions. For example, a pale blue blouse under a woman's dark gray suit can subtly soften a look. A splash of bright, bold color conveys authority, and can be great for managerial positions. However, limit the number of brightly colored items to one, and make sure it is not the dominant color of your outfit.
Brown - Brown is a neutral color that evokes feelings of calm. It is a great solid, neutral color for any interview.
Blue - Blue, particularly navy, is another great neutral color for interview outfits. Blues convey feelings of calm, trust, and confidence - great qualities for an interviewer to sense in you. Darker blues (like navy) convey authority and confidence. Blue is also many people's favorite color and wearing an interviewer's favorite color will always make a great first impression.
Gray - Gray is another great neutral color for interview outfits. It evokes sophistication and neutrality. Gray is a great color to wear as a suit or dress; it allows you to look powerful, but is not quite as domineering as a black suit or dress.
Black - Black is a very popular color for suits and dresses in interviews. However, black is a very commanding color that conveys a lot of power, authority, and even drama. This is a good color for a job in a conservative environment like a law office, or for an interviewee applying for a high-level executive position. However, black can be a bit overwhelming in a more laid-back office environment, and can make you appear unapproachable. Using black as an accent color can give you a bit of that sense of authority without being overwhelming.
Red - Red is a bright, powerful color that conveys energy and passion. A pop of red convey just the right amount of passion without making you appear too emotional.
White - Crisp and clean, white is a great color for shirts and blouses. The color conveys truth and simplicity, and adds a bit of brightness without being too overwhelming.