Double curtains.
The scene contains a simplified window model.
The color of the model can be easily changed in the material settings.

For Corona render, it is recommended to install version no lower than 1.5, since the glossiness of the materials is adjusted taking into account PBR.

If you are working in a V-Ray version lower than 3.1, then be careful, in the materials in the BRDF section there is Microfaset GTR (GGX), if your version is older, then the BRDF field will be empty. Choose Blinn, Phong or Ward - whichever is preferable for you.