Your opinions about KOETSU URUSHI BLUE or VERMILLION

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.

Well the differences in Koetsu builds are always shrouded in a bit of mystery. I don’t have any experience with any Urushis or the Black, but I do have experience with the RSP and a number of stone bodies. The differences in stones like Jade vs. Onyx are pretty subtle and hard to even describe. The magnet type (Platinum vs. Alnico - I have the Alnico from an older Onyx Gold/Signature I had rebuilt) has a much bigger sonic impact. The Alnico magnet also has double the output level. The cantilever, diamond vs boron also has a much bigger sonic impact - the DC increases detail, clarity and dynamics without any obvious downside. The RSP (it has a clear lacquer, which I believe is missing from the lower Rosewood models) has less bass impact and power vs. the stone-body platinums, but the magnitude of this body difference’s impact is certainly less than that of magnet type or cantilever. And then you have the top-range Coralstone and Blue Lace stone models, which even with boron cantilevers seem to be a little "better" than the lower-ranked stones somehow, but it’s hard to say if this is due to being granted the "best" hand selected motors, and/or possibly getting slightly larger magnets (they seem a little bit higher in output, too) - no idea for sure, though.

In picking Urushis, the big choice is Vermillion vs. anything else. Again, I’d advise a proper SUT for the Vermillion (I like SUT’s with all Koetsus anyways, but that 0.2mV output will be especially tough without a SUT - and the Hashimoto HM-7 are fantastic with Koetsu, highly recommended). If you choose the non-Vermillion Urushis, just pick a look that pleases you! I think all the Urushis are beauties, and I'd love to try one someday. Probably would not be a Vermillion though, because even with a good SUT noise floor can creep in at that level.

In fact everybody is talking, but no one knows really how a vermillion sounds.....

Just curious, why Koetsu is so expensive, what is the technical advantages? I remember Garrott brothers, who rebuild them and retipped them for the clients, often commented about poor build quality of those cartridges (made at that time by Sugano-San himself). Now it's not even Sugano-San ...  

Even lower model are extremely expensive compared to many great cartridges with reputation. 

I have never owned any of them, but i wish to know