How to colorize particles based on x-position?

[Mnietek]

How to colorize particles based on x-position?
I try with Custom properties operator and Mapping operator. 
   

And this work for particles which x-pos is greater than 0:
   

Why doesn't it work for X<0?

[tyFlow]

Don't use a custom vector for this - use a custom float (there should be a 'position X' property available).

When you normalize a vector you're normalizing its length, which won't get rid of the negative values, leading to the unexpected result.

[Mnietek]

Thanks - that way is better.
But what values should I use as normalize values?
I try with min and max values of particles X-pos but can't get gradient from white to black...

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Ok - i thing this is a v-ray problem.
When I set SubChannel to All in Vertex Color map every thing is OK.
Proviously that was set to Red subchannel...