I would definitely call the installer and have him make it right.

You can certainly contact him now, and I advise you to do just that. But prior to treating the grout with anything give it about a week to dry out.

There can be residual moisture from the thinset still behind the tile. That can wick into the grout and cause blotchy grout.

The white dust could indeed be "tile dust". Or just a haze. Or efflorescence.

I'd also advise you to give Laticrete's tech department a call. They can offer you advise if it's haze from a sloppy water cleanup, of efflorescence. See what they have to say, that could give you some ammo when you talk to the tiler.

I recommend you read this.

Then call 1.800.243.4788 ext 235 if you have other questions.

Good luck!

Thanks! The document is definitely helpful.
I know I can spend some extra bucks to get phosphoric or sulfamic acid and then may be also buy epoxy colorant, but then if it's installer's fault he should be fixing it without additional charge? Isn't it?