A stroke of blue in somebody's aura is an indication of a strong psyche, however one that may be a bit in the clouds. Those with a lot of blue in their aura work more in the psychological domains and have to make sure to ground themselves, however they can be very insightful.

Blue is the colour of the throat chakra, overseeing articulation and truth. IF your throat chakra is clear and streaming, the blue in your aura would imply overt gesture of the knowledge you hold inside.