Without knowing your teacher, here's what I believe she means:
Try looking at some vivid, colorful object. Stare at it hard for at least half a minute without looking away. Then close your eyes. Inside your eyelids, you will see a residual image of the object you were staring at, and the image will be a different color than the real object is--like a photo negative in pre-digital photography.
I think that's what your teacher is talking about. Note also that things we look at may leave some "impression" on our sight even _without_ closing our eyes.
Try looking at some vivid, colorful object. Stare at it hard for at least half a minute without looking away. Then close your eyes. Inside your eyelids, you will see a residual image of the object you were staring at, and the image will be a different color than the real object is--like a photo negative in pre-digital photography.
I think that's what your teacher is talking about. Note also that things we look at may leave some "impression" on our sight even _without_ closing our eyes.
