Each basketball game has two or three officials. In every officiating crew, there is one head referee (sometimes called the crew chief). The remaining officials are called umpires, though you may often hear them simply referred to as officials. While there is a title difference between these officials, there are very few differences in their roles.
To review, the titles of official, referee, and umpire are as follows:
Both the referee and umpires are allowed to call all types of fouls and have jurisdiction over all phases of the game. During play, the referee starts along the baseline, with the umpires taking the trail and center positions. This will change throughout the game, though. Every official is expected to be able to operate from every position on the court and make calls as necessary.
Though uniforms may vary depending on the league, an umpire's uniform is very simple. They typically wear black pants, black sneakers, and a white and black striped shirt. In leagues like the NBA or WNBA, an umpire's shirt may include the league's logo and some personalization.
They will also need to have a whistle as part of their uniform, in order to stop gameplay and make calls.