Tan is a good window color, neutral. This neutral color will easily go with almost anything you choose. Typically the trim in a home is all the same color. If your base, casing, doors and frames are white or light off white then this color is best for the trim around your windows. As a way to "accent" the windows consider painting the doors the same color and the frames the main trim color. Maybe try this in one room and see if you like the look.

As mentioned the color is neutral so the walls can be a darker shade if you like the look. You don't have to stick with tans. Many nice colors will easily go with the windows; olive greens, golds, browns, etc. Make sure to test each wall color you want to use, sample paint is cheap while the labor to apply the final chosen color isn't.

Hope this helps.