In chapter 12, we first know that the Giver agrees with Jonas in disliking sameness when the Giver simply responds "it is" after Jonas expresses his appreciation of the beauty of the color red. In this chapter, Jonas has just understood for the first time what color is, and he immediately wants to know why everyone can't see it. Through the Giver's statement, we see that he too appreciates the beauty of color and of differences.

The Giver tries to explain further, giving Jonas an even-handed explanation of the situation in the community, laying out the facts for him. He explains that the people of the community made the choice to go to sameness a long time ago, and that they got rid of color, sunshine, and differences in order to have greater control over things. He further explains that the community had to let go of some things in order to gain that control. The Giver is trying to give Jonas an understanding of what happened to the community without expressing his opinions, but Jonas immediately knows what his own opinion is.

The Giver also reveals that he agrees with Jonas about his dislike/distrust of sameness when he says,

Maybe your wisdom will come much more quickly than mine.

He says this in response to Jonas's impulsive statement ("We shouldn't have!") after the Giver explains to Jonas how the community did away with differences.

In chapter 12, Jonas again experiences what he calls "seeing-beyond." Jonas first witnessed this phenomenon with an apple; he notices a considerable change in the apple but cannot describe it. The apple stayed the same shape and size, and he can't point to the modification. Jonas now has a similar experience when he interacts with Fiona and sees a change in her hair.

Jonas relates his experiences to The Giver, who brings him back to his memory of a sleigh ride. In this dream, Jonas again sees-beyond, as the sled changes underneath him. The Giver explains that Jonas is beginning to perceive the color red. The vibrancy of the red color is difficult for the genetic scientists to completely erase—they have yet to "master sameness." Jonas and The Giver live in a colorless world, where no differences are permitted to exist.

I think there are a couple of things that the Giver says that clue the reader in to the notion that he does not like the Sameness. With that said, I think that one of his statements more clearly shows his distaste for the Sameness than the other statements. The quote comes fairly late in the chapter, and it is in response to Jonas vehemently stating that the community shouldn't have let go of all that they let go of in order to adopt the Sameness and control so much.

"But we had to let go of others."

"We shouldn't have!" Jonas said fiercely.

[. . .] "You've come very quickly to that conclusion," he said. "It took me many years."

That statement lets readers know for sure that the Giver has the same conclusion and thoughts about the Sameness as Jonas has. Prior to him saying that, the reader might suspect that the Giver doesn't like the Sameness, but he isn't necessarily giving anything away. He attempts to stay quite neutral in his explanation of what the Sameness is, how it works, why it was adopted, and the pros and cons of the Sameness.

Jonas learns that the community once had colors, and The Giver explains to him that they gave up too much for Sameness.

The Giver teaches Jonas about the Capacity to See Beyond, which means in his case that he can see the color red.  Color was one of the things the community gave up in the switch to Sameness.

The Giver chuckled, suddenly. "We've never completely mastered Sameness. I suppose the genetic scientists are still hard at work trying to work the kinks out. Hair like Fiona's must drive them crazy." (Ch. 12)

The community does not allow anyone to be different.  People have the same skin tone, and the same hair color.  They even have the same eye color. Everyone in the community has the same dark eyes, but Jonas’s are light-colored.  The Giver and baby Gabe also have these light eyes.

The Giver shows Jonas the memory of the sled again, which is the color red.  Jonas says that the color red he saw was beautiful, and The Giver agrees.  He tells Jonas that getting rid of colors was part of the choice to go to Sameness, which meant gaining control, but also giving up a lot.

"Our people made that choice, the choice to go to Sameness. Before my time, before the previous time, back and back and back. We relinquished color when we relinquished sunshine and did away with differences." He thought for a moment. "We gained control of many things. But we had to let go of others." (Ch. 12)

It is clear that The Giver does not completely agree with the choice the community has made.  Sameness meant everyone feeling comfortable all of the time, but it also meant giving away beautiful things and pleasant things along with the terrible and unpleasant ones.  He explains to Jonas that it took him years to come to the same conclusion Jonas did, that Sameness was not all it was cracked up to be.

Jonas is told that he will acquire wisdom with the memories.  The Giver explains to him that part of that wisdom is in understanding the community’s faults.  Until now, he has done nothing but accept unquestionably the community’s rules.  As he experiences the memories, he learns that the community is not the perfect world he thought it was.