Like it or not, we subconsciously judge people in less than a second (trust worthiness, attractiveness, etc.). It's a survival mechanism in humans. Clothing specifically is a representation/expression of your thoughts/character/personality.
The color, the type of clothing, how revealing it is, accessories, etc. all play to build an image/impression when first interacting with someone. This person will then take this judgement and approach the interaction with that judgement (also depending on their EQ and how quick they are to judge. etc). Great question!