Because blue light is absorbed and it do not reflects red light reflect back . so the short appears black

A piece of cloth appears red in sunlight. How will it appear when held in the blue portion of a spectrum?

When a piece of cloth appears red in sunlight, it means that it primarily reflects and absorbs certain wavelengths of light. The perception of color is based on the interaction between light and the object's surface. In this case, the cloth is reflecting predominantly red light while absorbing other colors.

Understanding Light and Color
Light is composed of different wavelengths that correspond to different colors. When white light, such as sunlight, passes through a prism, it gets dispersed into its component colors, creating a spectrum. This spectrum ranges from red to violet, with red having the longest wavelength and violet having the shortest.

Reflection and Absorption of Light
The color of an object is determined by the wavelengths of light it reflects and absorbs. When light strikes an object, it can be either absorbed, transmitted, or reflected. The colors we perceive are the result of the reflected light that reaches our eyes.

The Color Red in Sunlight
When a piece of cloth appears red in sunlight, it means that it predominantly reflects red light. This occurs because the cloth absorbs most of the other colors present in white light, such as blue, green, orange, and yellow. The red light is reflected back to our eyes, creating the perception of a red color.

Appearance in the Blue Portion of the Spectrum
If the cloth is held in the blue portion of the spectrum, the way it appears will be influenced by the wavelengths of light it reflects and absorbs. Since blue light has a shorter wavelength than red light, the cloth may not reflect much of the blue light and instead absorb it. As a result, the cloth may appear darker or even black in the blue portion of the spectrum.

Conclusion
The appearance of the cloth in the blue portion of the spectrum will depend on its ability to reflect or absorb blue light. If the cloth predominantly reflects blue light, it may appear blue or bluish. However, if the cloth absorbs blue light, it will not reflect much color in the blue portion of the spectrum, and it may appear darker or black. The specific appearance will vary based on the cloth's material and how it interacts with light.