It is a colour that has long been associated with sadness, but blue in a child's drawing actually means they are feeling happy, a new study suggests.
The research claims the colours children use reflect their mood and feelings about the subjects they are drawing.
When asked to draw something they saw as nasty, they typically reached for the black, brown or white crayon - although older children also used pink.
The experiment involved 253 children, aged four to 11, who were asked to draw figures which were neutral, nice or nasty. The researchers found that children drew positive subjects larger and in their favourite primary colours.
Yellow and red were the next most favoured colours, while for most children, green, orange and purple were seen as neutral.
The researchers hope the findings will eventually lead to a set of guidelines for professionals working with children and that they will be able to gauge a child's state of mind by looking at picture size, amount of detail and use of colours.
Dr Esther Burkitt, of Plymouth university, who carried out the research for her PhD, said: "I became fascinated with looking at how drawing could be used as a language in its own right. Kids are doing something when they draw - just like adult artists."
But she warned against making assumptions about individuals, who may use different colours to express different feelings - such as Picasso, who famously used blue for a series of images of melancholy and destitution.
Study co-author Dr Martyn Barrett, from Surrey university, said it was the first to reveal a robust link between drawings and mood: "Clinical psychologists and educational psychologists may want to look at children's drawings and draw inferences about how the child is feeling.
"This is really the first sequence of studies to do this sort of work with proper experimental controls built in. It is important because developmental psychologists who looked at previous studies said the conclusions aren't valid."