Blue. This was my idea to show my favourite colour. One white bristol board is laying on a glass table and another board is behind the glass with ice cubes. Ice cubes have food colouring added. Some more and some less for different shades. I cut a small hole in the bristol board on the table and taped a flashlight flush against the table. The glass has just cold water and ice cubes in it. All lights are off except the flashlight. Hope you like.