The Minions' usual overalls in the Despicable Me franchise are blue. Their blue denim-style clothing is one of the characters' most recognizable visual features, paired with yellow skin, gray goggles, black gloves, and black boots.
The Minions are small, capsule-shaped creatures who serve supervillains. Although individual Minions vary in height, eye count, hairstyle, and personality, the standard blue overalls help make them look like part of the same mischievous workforce. The outfit also gives them a practical, uniform-like appearance suited to their role as Gru's henchmen.
The color can change in special situations. For example, Minions may wear costumes, disguises, or altered clothing in particular scenes, and some films show them in different uniforms. Those exceptions do not change the canonical answer for their usual attire. Their goggles are commonly mistaken for the overalls' color because both are iconic parts of the design, but the goggles are gray while the overalls are blue.