Previous studies of affordance have not explored in detail how a special type of affordance -- institutional affordance -- worked in multilingualism. By drawing empirical voices of students, this study investigates how institutional affordance supplied by a collegiate multilingual education policy was perceived and utilised by students. A thematic analysis of data collected from ethnographic observation, narrative frame writing and semi-structured interview reveals that learners first carry out affordance perception screening and that those present in classroom learning opportunities are easily perceived, while those in forms of social and technological learning opportunities outside the classroom might encounter affordance blindness. However, a successful perception does not guarantee full utilisation; as learning continues, either full utilisation or abandonment of perceived affordance may occur depending on the dynamic interaction between learner agency and affordance. This article ends with suggestions to teachers, curriculum designers, and policy makers on how to improve collegiate multilingual education programmes from an ecological perspective.