godan verb (-ku), intransitive verb
change color; turn red/yellow
Primarily used for autumn leaves changing color; can also refer to other natural color changes like fruit ripening.
山の木々が色づき始めた。
The trees on the mountain have started to change color.
秋になると、もみじが美しく色づく。
In autumn, the maple leaves turn a beautiful red.
godan verb (-ku), intransitive verb
ripen and change color
Used for fruits and vegetables that change color as they ripen, such as tomatoes or persimmons.
トマトが赤く色づいてきた。
The tomatoes are ripening and turning red.
godan verb (-ku), intransitive verb
become sexually aware; reach puberty
Figurative use, often applied to young people becoming aware of romantic or sexual feelings; somewhat literary or euphemistic.
彼女もそろそろ色づく年頃だ。
She's reaching the age where she becomes aware of romance.