When was the last time you saw a paint colour at your friend's house and knew that was the one for you, bought the tin, painted a whole wall and then hated it. It just doesn't look the same. This may be due to the affect the lighting in your friend's house had on the paint.
Fluorescent lighting will give out a "cool light" and down lights a "warm glow". You also need to take into account how much natural light there is.
The best thing to do is to buy sample pots, paint an A4 piece of white cardboard or a canvas and when it's dry take it around the house and see how it looks in each room. Leave it in one spot on an easel or up against a chair and see how the colour looks at different times of the day.
