Yellow was the colour of the first standard LEGO minifigure released in 1978.
The modern LEGO minifigure debuted in 1978 with movable arms and legs, a solid head and a simple smiling face. Early figures were generally yellow-skinned, a design choice that allowed them to represent characters without assigning a specific real-world ethnicity.
The first minifigures appeared in early LEGO Town, Castle and Space sets. Their standardised proportions made them compatible across themes, so a figure could move from a police station to a castle or a spacecraft while using the same basic body system.
LEGO later introduced a much wider variety of skin tones for licensed characters and some other products. Yellow remains strongly associated with classic LEGO minifigures, but it is important not to confuse the original yellow colour with the date of introduction: the modern minifigure arrived in 1978, a fact separate from earlier non-moving LEGO figures.