The first thing to remember is that there are only three primary colours red, yellow and blue. The true group of primary colours are cobalt blue, cadmium red and cadmium yellow. All other colours are secondary colours and made from mixing the primary colours. For example red and blue make purple, blue and yellow give green and yellow and red make orange.
Download the outline of the house and tree to experiment with mixing colour, don’t be afraid to experiment. Once you are happy with these colours try swapping the cobalt blue for a lighter or darker blue but keep the red and yellow the same. See how this changes all the colours
Look at your paintings and see if one painting looks like a sunny day where as another may appear dark as if it is about to rain. This is how you learn to create atmosphere within your painting.