everyone's interpertation is different, so keeping track of what colors you see and what they were feeling can help in deciding what each color means.
what were you feeling then?
what do you usually feel when your aura was purple?
what was your biggest feeling during the day?
what do you usually feel?
did you do something different that you normally dont do? like a ritual, or going on a trip.
you coudl also look at the associations of the color. purple is calm and peaceful compared to a bright yellow.