The Spanish word 'rubio', meaning 'blonde' or 'fair-haired', comes from the Latin word 'rubeus' meaning 'reddish' or 'red-colored'. 'Rubeus' itself derives from the Latin verb 'rubere' meaning 'to be red'. This etymology shows an interesting semantic shift from the concept of redness in Latin to the modern Spanish meaning of blonde or fair hair. This shift likely occurred because reddish-blonde or strawberry blonde hair colors served as an intermediate connection between the original 'red' meaning and the current 'blonde' meaning.

Several common Spanish words share this Latin root relating to redness, including 'rojo' (red), 'rubor' (blush), and 'rubí' (ruby). These words maintained the original connection to the color red, while 'rubio' specialized to describe blonde hair color.

English has several words that come from the same Latin root 'rubere', including 'ruby', 'rubric' (originally referring to red ink used for important text), and 'robust' (which originally meant 'reddish' before evolving to mean 'strong' or 'healthy', as a healthy complexion was often ruddy). The word 'russet', meaning reddish-brown, is also related. These English words maintained various connections to the original concept of redness.