The colour yellow and keris
 

Many years ago when I first started getting into keris I remember reading that keris sajen were traditionally secured to the main beam of a house using yellow ribbon or cord to protect the dwelling.
For some reason this stuck in my memory and I would notice throughout the years that whenever someone was making claims of an object being mystical be it a keris or a stone they would always keep it wrapped in yellow cloth, have a yellow string/rag attached to it or keep it in a yellow cloth bag.
Also in Silat yellow is considered a color of protection and is often worn by those who practice silat.

So what is it with this colour yellow, anyone have any deeper explanation for this tradition?

I have a special form-fitted box for storing one of my keris, the lining of which is yellow silk. I believe this is a standard color for such boxes.
We might look towards Hindu symbolism as a source for this. Yellow is the color for Vishnu and represents knowledge and purity, so that would make a lot of sense as a color to wrap an heirloom keris in.

In China also Fu are always drawn on yellow paper, just an observation.

Well, it's also the color of the "smiley face" :) , but i doubt there is any connection there… ;)
It seems more likely to me that symbolic practices pertaining to keris would be more likely to originate with the culture that developed the keris itself.