Thanks for your question. My general rule of thumb when it comes to dress codes for an interview is that it is always better to be overdressed vs. underdressed. Thus, even though your interviewers may be in very casual clothes, you should still probably attend your interview wearing a formal suit. Even if a recruiting coordinator tells you it is okay to dress less formally for an interview, it is always safer to go with a more formal outfit.
Remember, you are primarily the one who is being evaluated so it is important to look your best. Dressing in a suit will also make you feel more professional and polished. It also shows your interviewers that you are taking their meeting seriously and that you respect their time.
In choosing a suit, be sure to pick neutral colors. Navy blue or black are always solid choices. You may have a fantastic fashion flare, but an interview is not the time to display it. For men, simple yet elegant ties in traditional colors will be well-received. If you are choosing between two potential looks for an interview, go for the more conservative one. In addition, choose dress shoes that are more formal and would not be mistaken for a more casual shoe. You want to make sure your visual presentation of yourself is as strong as the professional one you will be making during your interview.