Blue ice occurs when snow falls on a glacier and is compressed so that it becomes part of the glacier. During its journey down the glacier, all the air bubbles are squeezed out and the size of the ice crystals increases so that they become brighter. The ice is blue for the same reason that water can be blue, namely because of the absorption of red and yellow light so that blue light remains. So the pieces of blue ice floating around Antarctica have quite a history behind them.