A dress code (//) is a set of expectations, either formally or informally defined, regarding appearance, particularly clothing but also including personal grooming such as hairstyles.
Dress codes can range from "wear whatever you like" to requiring you to wear a 2 or 3 piece suit to high end business clients.
In some countries personal tailoring is readily available. In which case bold colours and patterns can be great.
Note if you're a manager, and your company specifies dress codes for your staff, those staff will notice if you don't follow it yourself.