Window treatment is not an afterthought. Well chosen drapes and shades will frame and mask your outlook, create a cosy ambience, filter the light and offer much more. It is especially important for bedrooms where privacy is important. In the living room, it may be dispensable but it is advisable to have at least day curtains to reduce glare and render a soft touch to the room.
A curtain wall i.e. a generous drape running from one end of the wall to the other, is prefect for creating a new 'wall' when you need one in the room. This could be due to the presence of shallow beams and columns, making positioning of furniture difficult, or you need to conceal an awful permanent feature - think awkwardly positioned or badly proportioned windows - in the room. In the example below, a dark suede curtain covers one of two sets of windows to provide a headboard back wall for the bed as there are no other solid walls around.
Tall windows look best with curtains. At areas with bay window and overhead beam, roman shades, roller blinds or venetian blinds look best s this avoids the 'mini-skirt' effect with short curtains. Avoid half height curtains (I know your windows are only half height) at all cost!
If you are unsure of the right colour for your drapes or blinds, try hanging a fabric sample (about a square metre) in front of the window to have a feel. If you aren't looking for a huge contrast here, choose a curtain colour which match the tonal values of the walls - even if you're using a patterned fabric. Never rotate a patterned fabric horizontally as it will skew the tonal values. Pick a pattern or colour one or two shades lighter than the one you wanted, as this will help take into account the light from the window, which would invariably make nearby colours look darker.