Blue what ? ! ? Do you mean an object that appears blue in white light ? Such an object appears black in green light.
Under red light, the red fabric of the jumper appears bright while the green fabric appears dark. Since black absorbs all colors of light, the green fabric appears black as it absorbs the red light, making it indistinguishable from the black fabric under red light.
A green object appears black when viewed through a red filter because the red filter absorbs green light, preventing it from passing through. Since the green light is blocked, the object appears dark or black because there is no green light reflecting off of it to be seen.
It appears black. A green pigment can only reflect green light and red light is a primary colour, that is it contains only red.
It appears black. A green pigment can only reflect green light and red light is a primary colour, that is it contains only red.
Green trousers appear black when exposed to red light because red light does not contain any wavelengths that are able to be absorbed or reflected by the green dye in the trousers. As a result, the dye appears dark or black.
The cap is called 'green' because it absorbs all other colors of light, leaving only the green light to bounce from it to your eyes. If no green light shines on it, then there's no light to bounce from it to your eyes, and it appears black. If you only shine blue light on it, then there's no green light shining on it.
A red object appears dark and almost black in green light because red objects absorb green light and do not reflect any light back to our eyes.
A green leaf appears green in daylight because it reflects green light and absorbs other colors. In red light, the leaf appears dark because it does not reflect red light well, as it absorbs more of the red light. This phenomenon is due to the specific pigments present in the leaf that interact with different wavelengths of light.
A ripe banana will appear black when illuminated with red, green, or blue light, as these colors are absorbed by the banana's pigment. Only yellow light will be reflected, making the banana appear black under the other colors of light.
The reason the wall appears black is that it absorbs light in the visible spectrum (~400nm to ~700 nm in wavelength); otherwise, the wall is no longer black. A green wall reflects green light (~500 nm) but absorbs all else. ===========================
The paper appears black. -- The paper is called "green" because it absorbs any light that isn't green, and reflects only green light to the observer. -- The filter is called "red" because it absorbs any light that isn't red, and transmits only red light through to the other side. -- There's no red light shining from the paper into the filter, so there's no light leaving the filter. The paper appears black.