Blue is the coolest colour - the colour of the sky, ocean, sleep, twilight A pure blue is the colour of inspiration, sincerity and spirituality. Blue is the calming colour. Blue is so soothing that is a good choice for pajamas. Dark blue is the colour of truth and moderation. A blue iris means your friendship is very important to me. Wednesday's colour is blue. Blue gemstones to wear to feel calm are blue sapphire and blue topaz. Lapis lazuli and azurite are said to heighten psychic power.