The right curtains act as a frame for your window in much the same way as a picture frame does for a picture. They highlight the beautiful scene outdoors as well as keep the harsh light of the midday sun out of your room. To make the most of a window from a decorating standpoint, it's important to think about the colours of your curtains versus the colours of your walls. Selecting the right curtain colour will enhance the walls and the window.
Pick a decorating style. This solution offers one of the quickest methods for determining the colour of your curtains, because many decorating styles have colour schemes that are typically associated with them -- including dictating possible colours for accessories like curtains. For example, in the Tuscan decorating style, the walls often come in more muted tones like sand that has been enhanced with a Venetian plaster technique. Curtains bring colours like terracotta, burgundy or Mediterranean blue to this neutral palette.
Choose contrasting colours if you want the window area to stand out; this holds true for areas like window seats or large bay windows, where the window functions as a room focal point. To pull this look off, you might choose some rich cobalt blue curtains to contrast against your honey yellow walls.
Bring a feeling of nostalgia to your curtain/wall combination by introducing muted colours like greys. Lighter grey walls that play against darker grey curtains recreates the feeling of a black and white photograph without much contrast between the lights and darks. So that this combination doesn't become visually boring, look for curtains with interesting patterns like paisleys, stripes or the fleur-de-lis.
Gravitate toward analogous colours for a more subtle look. For example, if you don't want to have such a sharp contrast between the colour of your walls and the colour of your curtains, consult the colour wheel to check out the colours that stand next to one another on the colour wheel. For example, pastel blue and mint green are two analogous colours in the pastels. To use this to determine your curtain colour, you might go with a mint green wall with pastel blue curtains; make sure the curtains have a bit of mint green in them as well to tie everything together.
Don't forget other decorative elements as well. A painted wrought-iron tieback or decorative swag hung next to the window will help bring emphasis to this area and allow you to introduce your wall and curtain colour to the other decorative elements near your window.
Consider how the colour palette will affect the visual "temperature" of the room and what kind of cast it will throw on the room. For example, you might love those thick red, velvet curtains, but remember that too much red will cast a strange light on your skin; if the red curtains are for your bedroom vanity or bathroom, you may want to consider another colour for the curtains.