Why Shiva, Krishna & Rama are blue?

Blue colour signifies all-inclusiveness. We can see in the existence that whatever is vast or beyond our perception is blue in colour whether it's ocean or sky. Shiva, Rama and Krishna had blue aura not blue skin. 

First of all let's know what's aura. An aura is a certain field of energy around any substance. The whole existence is energy. A part of energy takes physical form and a part of energy isn't physical but has a form. That energy which doesn't become physical but has a form is called aura. 

So, maybe because of blue aura Krishna looked blue in colour. His aura was blue because of his inclusiveness. His blue aura made him irressistibly attractive. Even his enemies or the assassins sent by Kansa were mesmerized experiencing his aura. Poothna fell in love with him the moment she saw him. She got entangled in his blue magic. 

In Yoga it's said that one's aura has hues according to their saadhna or inner evolution. If we'll lay emphasis on agna in our saadhna then our aura will be orange. That's the colour of renunciation, aceticism and Kriya. A pure white aura depicts that the being is absolutely pure. Such a person's presence will be fantastic but he won't be all-inclusive and won't get himself involved in activities. When someone attains to his highest and decides to be active in world has electrifying blue aura. This aura makes people believe that the being is superhuman. We can relate this thing with Krishna, Rama and Shiva. 

Those who were aware of his true identity saw Krishna's blue colour & the unaware ones saw him as a dark skinned boy. The truth of life is more important than the facts of life because truth makes a difference but facts won't make any difference in our lives.