There are often three main parts of a red giant stage: firstly, the red giant's center is plain helium while the layer outside it has hydrogen fusing into helium. This is called the red giant branch or RGB phase of the star. Eventually, the helium in the center will ignite and start to turn into carbon. This ignition is called the helium flash, and after this happens, the red giant branch star becomes a horizontal branch star. For stars with the same mass than the Sun, the horizontal branch phase is called the red clump phase. Red clump stars are smaller and hotter than red giant branch stars, and can appear yellow or orange in color. For stars more massive than the Sun, they become much hotter so that their color will change from red, to yellow, and then to blue-white. Their horizontal branch phase is called a blue loop.