The beauty of underpainting is that it establishes a certain mood and atmosphere in a painting right from the start.  In addition, it can be the first step in a painting even if you don’t know exactly where or what you are going to paint.  In the painting above we have yellows, blues and greens in acrylic which were allowed to dry before adding another layer with a different medium.  It is a warm painting despite the coolness of the colours simply because these blues and greens are at the warm end of the spectrum and will contain a hint a red within them.  I didn’t know it would be a sky and sea at the beginning – I simply kept looking at it until it revealed itself to me.