Did you use a white undercoat first when you painted? Although you don't have to do this with a lot of paints, if you have a very dark colour that you need to paint over, it is better to use an undercoat first so that the darker colour won't shine through. On the Crown (paint) website:
http://www.crownpaint.co.uk/expcolour/create/ you can use a picture of the room you want to decorate or choose from the selection of rooms they have and then apply different colours of paint online to the walls, ceilings etc to see if you like the effect.