It is common to mix fabrics when it comes to window treatments because doing this gives the room an added dynamism that makes the design a little more interesting. By going a step beyond simply pairing colors with one another, offsetting a variety of fabrics also give you more freedom to implement different textiles in the furniture and decor throughout the remainder of the room.
When most people do this, they usually pick a heavy base fabric and pair it with a sheer. However, try pairing two heavy fabrics together. Instead of weighing a room down, it can anchor a space without overwhelming it.
A simple way to implement this style is by hanging a banded thai silk paired with a velvet drape from one of your window panes. These are two luxurious fabrics that when used on one treatment will elevate the formality of a space, so it is best to use these in a dining room or other fancy area of the home.
Pearl white silk and darker velvet, like a brown or other earth tone, will look clean when paired together and give off a modern interpretation of luxury. This will look good in a dining room inspired by contemporary design, which emphasizes chic linear decoration. Since these colors are more subdued than showy, you are demonstrating good taste but still displaying restraint.
Any room can be made warmer and more sophisticated when it is infused with a whole medley of fabrics and colors.