Some of the confusion comes from the fact that most people don't know the difference between purple and violet.

For example, certain church vestments and decorations used in certain seasons are often called purple; actually, they are always violet.

Both violet and purple are a mixture of blue and red. Violet is more blue than red; purple is more red than blue and has the "plummy" look, whereas violet is more or less darker version of lavender and may be very dark indeed -- almost navy.