So, objects are certain colors because they are absorbing every color except for that one. So why is it that if I take a projector and project a blue image on a red wall, the red wall still reflects the blue image rather than absorbing the blue light? I don't know if this is considered a dumb question, but I was thinking about it and it got me curious (also, I haven't taken any kinds of physics).


This is due to a psychological effect known as Color constancy. Your brain seems to see something based on the context around it, for instance the blue image projected on the red wall may be more black than blue but your brain will compensate for some of that because you also see the red wall.

This is also the source of a number of related optical illusions. For instance consider the image below taken from here. The squares labeled A and B are actually the same color, but one looks dark gray and one looks white because tile B seems to be in a shadow and surrounded by dark tiles and A is not so our brain perceives that B must be lighter.

Grey square optical illusion

Here's another optical illusion that may be closer to your question. The center piece in both images is the same color (gray) which you can see here.

enter image description here


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