No way to get EITHER darker section ( I see two and a half ) removed without wrecking the whole shower.

Removing all of it will also ruin waterproofing......making the entire shower a do over.

Three unopened boxes, suggests he didn't open ALL the tiles, assort and blend what is generally normal variation......and mix to suit you.

It is also possible you had two dye lots in one order. In any scenario, did he check, or ask for any input prior to install where

you MAY have been there to point out tiles to eliminate entirely or absorb into a whole?

As Jan has so aptly put it a big no unless you want to pay for do over. My guess 2 different dye lots but if the are actualy real marble it is a nautural stone with natural variations. IMO now you have niche put some pretty containers there and move on . next time all the boxes are opened and the layout figured out it migght eve be the the install material has not completley dried behind those tiles but unless this was disussed before install IMO not worth the fight