red apples
Black, or nearly so. The apple reflects only green light, the red filter only lets red light through, so nothing reaches the eye.
green
It depends on what kind of filter, e.g. a blue filter absorbs everything except blue light, so only blue light comes out, which is why the filter looks blue, and is referred to as a "blue filter".
A blue object would appear darker when viewed through a green filter because the green filter would absorb some of the blue light that the object reflects, resulting in a more subdued color.
Since the apple is green, it would absorb any light that is not the same color as the apple. In this instance, the apple would appear very dark or even black since there is no green in the red light you are shining on the apple. A popular science experiment involves a shoe box, a piece of colored plastic or glass, a few objects (such as the apple), and a flashlight. If a red apple is being used with a red filter, the apple would appear to be a bright red since the apple is also red. The red filter allows the red color being reflected off the apple to pass through. Switch the filter to a green one, and the apple appears black since the filter effectively filters out all colors except green.
Purple will the object be
It is dark red.
Objects appear to change through a color filter because the filter only allows certain wavelengths of light to pass through while absorbing or blocking others. This selective transmission of light alters the color composition that reaches our eyes, leading to a change in the appearance of the object based on the colors that are filtered out or transmitted.
If you look at a lamp through a red filter, the lamp will appear red. This is because the filter allows only red light to pass through, while absorbing other colors. If the lamp emits white light, which contains all colors, the red filter will block the other colors, resulting in the red appearance. If the lamp emits a color that is not red, it may appear darker or even black, as the filter will block the light from that color.
When you look at a lamp through a green filter, the lamp will appear green if it emits green light or reflects green wavelengths. If the lamp emits other colors, such as red or blue, those colors will be filtered out, making the lamp appear dark or black, as the green filter only allows green wavelengths to pass through. Thus, the perceived color depends on the light source's color and the filter's properties.
The blue shirt would appear darker and more saturated when viewed through a blue filter. This is because the filter would allow blue light to pass through while blocking other colors, enhancing the blue color of the shirt.
If light reflected from a white shirt passed through a red filter and then a green filter, the shirt would appear black. This is because red and green filters would absorb most of the colors from the white light, leaving very little to pass through. White light contains all colors of the spectrum, so when most of it is absorbed by the filters, the resulting color appears black.