Your opinions about KOETSU URUSHI BLUE or VERMILLION

Just be aware that “lifetime warranty” and such may not mean as much as it sounds for these basically 1-man companies run by out of shape older guys. At least the Japanese analog masters often live and work into their 90s :-P

My assumption was that all Urushi's are ''painted Rosewoods''.
This would mean the same generator but different ''lacquer'' which
would provide slightly different timbre in order to satisfy different personal tastes. My own experience is comparison between
Rosewood Signature and Urushi Blue. Curious because of ''the
 same generator'' assumption I was much more impressed with
the Blue than Rosewood. Not sure what to think about ''different
painting'' in the context of sound but I have never heard any other
Urushi and only know that ''our Lew'' is also very satisfy with his
Urushi. Ergo ''consensus between two members in our forum''
should be sufficient for the ''argument'' that those ''lacquers'' have
some influence. 

And what about the vermillion, how does it sounds ?

Koetsu's may vary a little one to another even of the same model. then there is the set up and toenarms used. The paint used has absolutely no influence on the sound. 
Mulveling is right! I did not know this but the Vermillion has a different coil and is lower output so the phono amp is going to have to be a very quiet one or an SUT will have to be used. It might be a little more detailed due to the lighter coil but might not be a punchy for rock and roll.
Andy, you can add weight to your tonearm and it will work but you will never have the best bass a Koetsu can produce because you have a unipivot arm. These arms work better with more compliant cartridges. I can highly recommend the Ortofon Windfeld Ti cartridge. It will track anything and is a great rocker. It is about the same price as the Koetsu and should not require adding any weight to your arm. There are also cartridges from Clearaudio and Lyra that would work although Lyra recommends against using unipivot arms with their cartridges.

So, as I suggested, one of the Urushi models, the Vermillion apparently, has a different coil from the others.  Thanks to whoever brought that fact out.  As to Mijo's blanket statement that the paint has "absolutely no influence" on the sound, that is conceivable but so far only one man's opinion, although stated as a fact.  However, you can find persons who say otherwise.  I would say that Urushi's do sound quite different from Rosewoods, based on 20 years of internet testimony from many different sources; the Urushi is said to have a wider subjective frequency response, better bass and more extended highs, compared to the base Rosewood, and there are other physical differences between the two types, besides lacquer vs no lacquer (or clear lacquer which might be the outer finish on the Rosewood).  Rosewood Signature or Platinum might be another kettle of fish.