cornish rock blue angel gin
This gin would certainly stand out on a shelf. The colour is not attributed to any particular ingredient by the distillery, however, a listing on another site mentions that the colour is all natural and derives from the 'blue gardenia' plant. However, blue gardenias do not exist outside of the 1950's film noir.
There is, indeed, a natural colouring (which is soluble in alcohol) called 'blue gardenia', which comes from the fruit of the same plant. It's this which is likely used to create this deep blue hue.
The recipe for this gin includes grains of paradise, seeds of a plant within the ginger family that provides a citrusy black pepper spice.