By the time a child enters kindergarten, his art has evolved from the scribbling stage into what is known as the 'pre-schematic' or 'pre-symbolic' stage. In other words, his scribbles actually begin to look like the real-life things that inspire his creativity. This is a big step in a child's development.
When a child has entered this stage, he makes the transition from just going through the motions of creating "art" to consciously drawing or painting something in its likeness. Typically, the first image attempted at this age is a person. This 'person' is usually drawn with a circle for the head and two long lines for the legs. Before you know it, these images become more developed--including other body parts such as arms, hands and feet as well as other details such as hair and clothing.
And while your child's artistic abilities are developing at a rapid pace during this time, color still doesn't have much meaning in art at this level. When a kindergartner draws something he tries to match the shape of the object, not the color. He thinks more in terms of the space that surrounds him than in terms of the shade and texture of that space. The sky is above, so he draws a line at the top of his page, the ground is below so he draws a line at the bottom of the page, and everything else is drawn in between these two lines in the fashion of floating around the page. So it's perfectly normal if that sky is filled in with green and the grass, with blue. Even Michaelangelo started out this way.
As a child develops and improves in his abilities in art, the more the child is able to come up with different ways of creating images. Art has become a way for him to clarify his thoughts and communicate his thinking. The pre- symbolic stage is an important step on the path to communicating. It is this communication through art that leads to communication through the written word.