White light is made of the “primary colors”. What I’m saying is the reason why you see a purple surface as purple is not because purple light is being bounced back. Rather it is because green light is being absorbed so red and blue are bouncing back and red and blue makes purple. Therefore if you would shine a light through a filter that filters out everything except blue light then the blue light will reflect back and you will see a “blue shadow” under the filter. The surface wasn’t absorbing the blue light it was just mixing it with red so you saw purple. The premise that your question is based on assumes that the surface was absorbing the blue light.
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