Your aura consists of seven - nine auric layers (also known as bodies or planes), and each one represents something different. Think of them like the layers of the onion, with the middle being your physical body.
As its name suggests, the physical aura plane is the layer that represents our physical health. It's the layer closest to your skin. It's also called the etheric plane (like 9 ether beings)
The colors of your aura correspond to one of the seven main chakras: root, sacral, solar plexus, heart, throat, third eye, and crown. Your aura is connected to these chakras, and is composed of the aforementioned auric layers. Knowing which colors correspond to which chakra can help you interpret what your aura is telling you.
Blue