To add color to the clipping mask, go to the layers panel and click the arrow beside the layer to reveal the other layers below it. Look for the ellipse layer (clipping mask layer) and select it. Select it by clicking it and then clicking the circle to the right. When you do this procedure, you will see the outline of the circle on the canvas. Go to the color pallet on the right and click a color and the ellipse will get a color.