Hi,
He did not put a chunk of pipe at the top as you state; the chrome part is the tailpiece of the lav drain popup. What you should do is order a popup that's of the same finish as the bottle drain, OR (worse alternative) move the drain rough-in up two or so inches so less of the tailpiece shows. When you order the new popup, order from the selection specially made for pedestal and vessel sinks, then your brass-colored bit will also be plated to match. Expect to pay about $50 up for this component.
It looks really good, BTW.
Casey

Oh! Wow, many apologies to my plumber!!!

Actually, he's here right now working on the kitchen valves. He said he didn't install the bottle trap originally because he didn't notice it amongst all the boxes of faucets and shower controls and whatever!! He has indeed installed them before. So double-many apologies to him!!

Okay, so I just need a new popup drain assembly?? I used the drain that came with my LaToscana faucet - the faucet is brushed nickel, so I assumed the drain would match, but I guess it wouldn't if they assumed it was going inside a vanity or something...

This is great information. Thank you, sombreuil_mongrel!!

A kind of alternative would be some matching spray paint, in case the brushed nickel proves too hard to find. It might be worth a try. Mask everything off better than you think you need to- overspray goes everywhere.
This is why I don't regret giving in and doing chrome. Some friends of mine had a similar difficulty doing a clawfoot bath and getting the supply lines, valves, everything exposed in the brushed finish. They had chosen a European brand, which added in a language barrier. They eventually got it worked out, and I'm sure you will also.
Casey

We identified the part I need (though I want to call Kohler to confirm it's the right one). It's a pop-up drain assembly with a thing sticking out the side. Comes in brushed nickel. There goes another $160.

Shoulda stayed with the Toto wall-mount sink with siphon cover (half-pedestal). Tiny, and no counter space for toiletries, but SO much cheaper than all this is ending up costing me!!! (Slapping myself - it'll end up looking gorgeous and be way more functional. So what's my problem.)

Thanks again!

SO - life is never so simple as it seems. I called Kohler to check if that drain assembly would work. The answer is: not the way I'd like it to.

See, my faucet is not Kohler. I bought this beautiful LaToscana Elba faucet that I fell in love with at Expo (looks a lot like the Kohler Purist but with the stick coming out of its forehead rather than out of the top of its head). Then I wanted a bottle trap, and the Kohler K-9035 was a good style-match, so I bought that.

If I replace the drain assembly that came with the LaToscana faucet with a Kohler drain assembly, the drain lever at the back of the faucet won't work. One of the Kohler drains has a lever that will stick out under the sink. The other uses a push-down/pop-up mechanism. I don't think either of these actually has brushed nickel tailpieces - it's just the drain part that appears at the bottom of the sink that's brushed nickel. The technical rep at Kohler told me the tailpiece isn't all that shiny, and some people rub it down with a scouring pad to make it look more "brushed".

I don't like losing the functionality of the faucet's drain lever - seems kind of hokey for an expensive new bathroom installation! I suppose this same problem would be there for non-Kohler drain assemblies (though maybe that would solve the problem of the tailpiece not really being brushed nickel). Best would be if LaToscana sold a replacement drain assembly, but I don't see one on their web site.

?????

I agree with sombreuil about trying the spray paint. What have you got to lose?
I've seen brushed nickel spray at Home Depot.

AND the bathroom is lovely btw!! The trap is a little detail.... it will all work out fine and is already beautiful.