Is it violet or indigo? They are 2 different colours. Violet is the colour of the crown chakra, indigo is the colour of your sixth chakra. Indigo is what happens when you blend blue and violet together, which is why it appears in the spectrum of light in between those two colours.
Depending on which colour it is, it may mean the respective chakra is very active and your astral sight is improving. Focus exclusively on it for a few minutes every day and see what happens.