I think there is an overall limit to going the "boring" option.
Yes, you should be known for poise, intelligence, ability to articulate your thoughts... but like most of us experience again and again, most of the applicants are also like that. That's where standing out in appropriate ways is key.
Ideas I tend to use include: a basic colored suit (black, gray, navy, tan, chocolate brown, a nice subtle pinstripe) with a "fun" top (if going with patterns, not too flashy, if going with lace, completely lined) that has a suitably high neckline (you can lose credibility fast by showin' off some cleavage). Other fun ideas include a pop of color via shoes, nail polish, a bracelet or an understated necklace... but pick ONE of those, maybe two if the color is subtle. I think the key is POLISH. Applicants to positions (grad school and internship) can show their ability to present in a professional manner when they come across as polished.
This lets your personality shine- which is a big part of determining fit! When you look boring, bored, uptight, uncomfortable, etc... that could be read as reflective of you. When you can have appropriate fun with it, it can allow them to picture a little more of how you would be as a trainee.