It is important to take into account not only colour of the curtains, but any issues such as light, warmth or style of the room(s).
A major issue could be, a north facing room, with windows that are not that large. In this instance we would need to maximise any light coming into the room. Maybe we would have the curtain track slightly longer than usual, thus enabling the curtains to pull back further and therefore allowing the maximum amount of light to come in. If the windows were quite small, maybe roman blinds would suit and by mounting them on the wall someway above the window, again this would allow in as much light as possible.
Blackout lining is excellent for cutting out any light coming through the curtains or blinds. This is especially popular in a young childŕ˘Ľdroom if they wake up as soon as it is daylight.
Maybe the windows are not double glazed. In this case, it would be worth considering having the curtains interlined. This not only helps stop draughts, but also gives the curtains a sumptuous look and feel with the extra thickness. Some popular fabrics at the moment are quite light weight, e.g. silk. These also need interlining to give a fabulous effect.