The colour blue used in traditional houses would mean they carry symbolic, spiritual or medicinal values and not merely for aesthetic appeal. Generally, it is said that cool colours signify  sereneness, peace, love and other gentle triats possesed by humans. Thus, when used for the painting of doors and windows, it could mean that the residents there are peaceful people. It is probably a flagmanship of unity and dislike for chaos and wars. 

Thanks Dickson. I agree with your last point. This is what I was thinking of may be a reason. As it can be a symbol of peaceful natives during the British rule. But there may be some scientific reasons too for which I am searching of if any body has any clue. Why blue does it help to trap heat or it keeps wild animals away from it (may be) why blue?

I have also noticed a tendency to use blue or blue green for doors and window shutters in many Arabic countries.  If it was green I would suspect a religious declaration but I cannot find a religious/cultural reason for blue, and I suspect that the blue green is more associated with the blue part than the green.  Given the association of blue with the sky/heaven it may just be that the custom arose independently of painting the liminal aspects of a house blue.  I am not sure that in this case we can rely on modern knowledge of the people who are still painting their windows and doors blue since in many cultures the original reasons behind why something is done have been lost meaning that ancestral motivations have to be reconstructed from literature rather than relying on local knowledge.

I agree with you and you are right Timothy the original reason behind why have been lost 

The most important books about colours are by Michel Pastoreau (e.g. Les signes et les songes, études sur la simbolique et la sensibilité médievales). I suggest you to read his work.

To what? Co's far a frage?

Vos far a frage?

Hi

The common ideas and beliefs associated with the blue color of some peoples are the color of envy. We have often heard stories that indicated that blue eyes are the most enviable, and we have often heard about a blue bead used by many people. As a response to envy, as a kind of response to the power of color effect in the same color used as a talisman.

In Britain it is usually green that is associated with envy, e.g. calling jealousy 'the green eyed monster'.  Although there is some room for overlap since green and blue often depend on the subjective opinion of the viewer, indeed in some languages, e.g. Welsh, the same word can be used interchangeably. 

It may happen that during british era as well as post independence that the trend started. 100 years back, the number of building painted blue were less. Cow dung or calcium carbonate with (blue neel) was used or some desi oils also or some local stones colour say geru, chuna or golu etc.. It is just a trend. Many school doors or buildings might have been painted blue without reason or as per availability and trend started in last 50 years or so. but now a days there may be variety of colours. Still green may not be favoured as mountains are already green.

Thank you all for your valuable suggestions

Friends soon I am going to answer this question in my accepted publication named as " Why Only Blue in the Traditional Architecture of Western Himalaya, India?" This article which is going to be published soon in Color Research and Application journal would answer this popular question. Will forward you the link as soon as published until then you too keep checking.

Best wishes

Ultimately I have got the answer to this question

Article Why only blue in the traditional architecture of western Him...