Roman blinds with fabric overlay for arched window.

The color of the curtains is edited in the material settings.

Other models of roller and roman blinds: https://3dsky.org/collection/shared/5237728 

For Corona render it is recommended to install version not lower than 1.5 since the glossiness of materials is configured taking into account PBR.

If you are working in 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. Select Blinn Phong or Ward – what is preferable for you.