A student purchased unripened tomatoes from market which were green in colour. After few days he noticed that colour has been changed to red

A student purchased unripened tomatoes from market which were green in colour. After few days he noticed that colour has been changed to red.Next day he asked her teacher about the reason.What could be the possible reason according to you ?

Green colour is due to the chloroplast and later on this chloroplast changed into chromoplast.