The aura is effected by many things such as death. Some would think death would present as black. Where as in actuality it is the fading of colors and aura altogether. This is your life force energy leaving the body.
When you are around people a lot your aura is effected by their aura. This includes the negative and positive energy. It is not uncommon for couples to have the same colors in their auras. Then when they are very in love to have a blending of auras.