Window treatments can an element of excitement or interest when they repeat colors or patterns found throughout the room. Used wisely, a multiplicity of patterns in a single space can energize a room with pulsating rhythm. Windows play a significant role in getting the job done, with the opportunity they afford for panels in one print and valances in another. The window fabrics need not be restricted to the windows only; often, they are found as accents elsewhere in the decor -- as throw pillows, comforters, bedsheets, or even wall borders.
But the two window fabrics don't have to literally repeat prints found elsewhere in the decor. By remaining in the same color scheme, they can take a bit of poetic license by mimicking other prints.
The idea is to pay careful attention to color, scale, and pattern, keeping all ingredients in the same family.