Final answer:
At 9 months of age, infants have a limited ability to see clearly, mainly light and dark.
Step-by-step explanation:
At around 9 months of age, the developmental milestone that occurs regarding vision is limited ability to see clearly, mainly light and dark. Although an infant's vision has improved since birth, they still have a limited ability to see small objects and have not yet fully developed perfect visual acuity. The ability to see colors and shapes develops earlier, usually around 6 months of age.