These lanterns can be found in Tenshukaku and at the Royal Hot Sprints. The fabrics have not been dyed per se, but have been coated by soaking them in a solution created by dissolving trace amounts of Amethyst Lumps and Electro Crystals in water. They say that this coating is not only able to increase the brightness of such lanterns, but can also protect them from lightning.
How to get Court Lantern: Thundering Heart?
Blueprint of Court Lantern: Thundering Heart can be purchased from Realm Depot for 160 realm currency.
After getting the blueprint, you can craft this furnishing using these following materials: