Hello again maat:
You are quite right to take this as the sign of illness or pain. It could mean just that. It could also indicate that your friend has a great deal of emotional problems or that there is an issue in their life that is causing them great emotional pain. Unfortunatly the colours in the Aura are not exact as some would have you beleive.
Try an emotional healing and see then if there are any changes.
I believe the person who coined the phrase, "That person has a dark cloud hanging over them", must have been able to see Aura's.
Everyone has light always.
...
/!\
Treewalker
