I would really go on the colours in the rest of the house. Are they cool and calm or bright and funky etc .... and whats the general feeling, mood that would describe your house. As the hall and landing are connecting the rooms - you kindof want it to flow. I would be inclined to look at the paints you have choosen. Look at paint leaflets and see what mood the colours you've got fall into then consider the other colours in that range/ tone. You could also go fairly neutral but use pictures wall hangings to connect to the rooms. Eg white hall and stairway with brightly coloured print at top.