Light colours generally add to the feeling of size and spaciousness. Dark colours can be depressing if there's isn't a window or a lot of light. Many of the DIY stores like B & Q sell mini sampler tins of paint. Why not buy two or three and experiment by painting a patches of each colour and see which you like best. Some of the "soft" shades, i.e. soft rose, soft blue, soft peach have a gentle warmth without being "in your face" in terms of colour. And these relatively neutral colours will blend better with your carpets.