According to the Dailymail, Travelodge had conducted a survey in the UK to find out which colours in a bedroom ensure the best quality of sleep. The results are indeed very helpful in designing bedrooms.
Bedrooms with blue colours tend to give the best sleep; nearly eight hours. It gives calm, soothing feelings and is thought to slow the heart rate and even reduce blood pressure.
While green and yellow come close, purple is truly avoidable in bedrooms. It is seen as too stimulating and can reduce sleeping hours to less than six. Grey and brown are complete no-nos for being too dreary and depressing.