The curtains on the windows of physics laboratories often have two layers, one is blue cloth and the other is red cloth. (1) What are the advantages of this? similarly

There are often two layers of curtains in the laboratory, one is blue cloth and the other is red cloth. Blue cloth can absorb light of other colors except blue light, and blue light reflected by reverse color is absorbed by red cloth, so light cannot enter the laboratory.

A layer of gray cloth and a layer of black cloth (two different colors)