It looks like they got a little black contamination or were trying a combination color match that went astray, but the overall color match and thickness looks good.

You used the dreaded "I" word - invisible. There is no such thing in the countertop seaming universe. It's "inconspicuous".

The bigger problem here is the color/movement match between the slabs. This seam is going to show no matter what.

Is it the seaming or the matching that bothers you? Can you take a shot from further back?

Some of the fill looks like a dirty stripe which would bother me especially as it doesn't seem necessary. Maybe they can redo that small area. Can't tell much about the matching.

Here's another photo. It's both the seaming and the matching that bothers me. They were trying for a combo color match.

It would seem if they lightened up the dirty part at the front, and mottled the color a little bit where that dark splotch further up runs into the light seam, that it would look pretty good.

Pretty counters!

I think they've made the seam more obvious & i'd ask them to redo it.