Your opinions about KOETSU URUSHI BLUE or VERMILLION

Andy, Koetsu's have nice warm bass if you put them in the right tonearm.
They are very stiff cartridges and require a tonearm with a high effective mass on the order of 18 to 20 grams. If you put them in a tonearm that is too light the bass will get rolled off and you might develop feed back. 
You can make a light tonearm work by adding head shell weights. In order to get this right you will need a test record like the Hi Fi News test record which has resonance bands on it. You add weight under you get the resonance point below 10 Hz but above 8 Hz. 
Which one to buy? Which color do you like? They sound exactly the same. My favorite Koestu is the Rosewood Signature Platinum. I use mine in a Kuzma 4 Point 14 which has an effective mass of 19 gm. The stone cartridges will work nicely in a lighter tone arm because they weight much more than the wooden cartridges. 

@millercarbon, back then is was "harsh or lush"? You're joking, right?

Dead serious. But its all a question of degree. Its all relative. That's not the point I was trying to make anyway. It was if you read it again "and this for what its worth is what he told me." So its paraphrasing not quoting but useful and something I happen to agree with- and not all that different than stuff Fremer has said- and so I put it in there.

They are very stiff cartridges and require a tonearm with a high effective mass on the order of 18 to 20 grams.

Please don't tell my Conqueror about this. It has no idea its not supposed to work so well. It might get upset. Or start slacking off, now that it has an excuse.

Many thanx for your answers.
 My turntable is a VPI ARIES 3 with JMW 10.5 tonearm, around 12gr it supposed to be.

If truly 12g it’s rather light so you would need use a heavier headshell or add weight as has already been stated.

But I have run plenty of arm and cart combos that theory and vociferous members insist would not work.
But they do sometimes so go figure.

However.....
Maybe consider something that is a better match to the tonearm though...