You forgot to mention the word ALMOST i used in my post. It's a hell of a lot easier today than it was 30+ years ago. It took a lot of skill to match colors then, it still takes some but with the color match systems they have now they can come pretty damn close.

Just last fall I had to get trim paint to match my new vinyl siding on my workshop, I took in a piece of siding and they matched it so close I couldn't see when I put a tiny bit on the siding sample I brought in.

Colors do fade or oxidise. But not from bright white to off white that the OPs later pictures show. And not that much in 2 years - which the OP also mentions. The contractor wasn't paying attention and is trying to squirm out of fixing it.