Baby blue as a colour designation for infant boys emerged in the early 20th century — a gendered colour assignment that was actually the reverse of earlier conventions (in the 19th century, pink was considered a strong, boy-appropriate colour and blue more delicate and feminine). The colour-gender assignment became standardised in the West around the 1940s.

Calm, innocent, and open. Baby blue is associated with the beginning of life — new, uncomplicated, and tender. It is among the most relaxing colours psychologically, combining the calm of blue with the innocence of pale tones. In adults, it triggers protective and nurturing instincts.

The pink-for-girls/blue-for-boys colour coding was not always standard — 19th century Western convention was often the reverse, or gender-neutral. The modern assignment emerged partly through the influence of the fashion industry in the early 20th century. "Something blue" in the traditional wedding rhyme predates this gendering — it originally referred to purity and fidelity (blue's association with the Virgin Mary) rather than masculinity.