Purple Raincoat in dreams
A coat that sheds water — preparedness for weather you know is coming.
How purple changes the reading
Purple colour places the symbol between hot and cool — a reading that has both calm and intensity at once. The dream often uses purple for symbols that do not fit the usual categories cleanly. Take the reading more seriously than you would otherwise; the colour is asking you to.
The base reading of Raincoat
A raincoat in a dream is the dream's image of the preparedness you wear when you know what is coming. The coat does not stop the rain; it stops it from soaking you. The dream brings the coat when you have, in your life, made the choice to prepare for difficulty in advance rather than be caught out by it. A raincoat on in a downpour is the dream telling you the preparation was correct. A raincoat left at home in clear weather, with a storm gathering, is the dream noting that you saw the weather coming and chose to travel without the protection you already owned.