Your opinions about KOETSU URUSHI BLUE or VERMILLION

One cannot meaningfully advice, suggest, or recommend a phono cartridge for a Music Reproduction System without knowing at the very least you're make and model of tonearm and you're make and model of phono preamplification it would also be helpful and instructional for you to reveal and explain why you have chosen a Koetsu cartridge many of which are hopelessly colored although that may be you're  style, taste, and preference

Yes your bass will be outstanding. Haven't heard the two you're looking at but I did have two Benzes before going to Koetsu and its a big step up across the board,  definitely including bass. Also I do have a 5 sub distributed bass array with superb deep bass, its actually now maybe the strongest aspect of my system, so if the bass coming off the Koetsu was deficient in any way it would be apparent. Its not deficient. Its awesome.

Koetsu is big money. I checked around a lot. The most knowledgeable experienced guy I could find has heard dozens of Koetsu's over decades and this for what its worth is what he told me. The reputation for soft lush euphonic yada yada goes back to the early original models which were indeed like that. A lot of this had to do with the fact that back then it was impossible to make anything like today, the capacity for refinement simply wasn't there yet, it was harsh or lush, at least by today's standards.

Since before his son took over the business though all that was gone. The son has moved things forward, with massive improvement in detail yet without ever crossing over into the hyped top end or other problems sensitive listeners experience with a lot of moving coils.

The sound you will get from either one of these will probably feel for you coming from a Benz the way it did for me. There were no big obvious changes in the sound. Koetsu is very similar to Benz, in the big picture. Yet you will soon feel its completely different in the way it brings the music right into the room. There's an effortless retrieval of subtle inner detail combined with authoritative control of dynamics that is darn near seductive. 

The difference between these high end carts as you probably already know is in these subtle refinements. For input specific to your Blue/Vermillion decision you might want to call Oswaldo. He is a Koetsu dealer, so take that into account. He has set up a lot of these and strikes me as genuinely caring about helping you find the right one. His number can be found here 
https://www.youtube.com/watch?v=AWp48WzlkMo

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.