According to this answer, the Trophy Room in the Tower Library is an Easter egg from the original Nier game and, like it, has statues of bosses you have defeated.
This trophy room is another feature of the original NIER, in which trophies representing all of the defeated bosses were displayed. This room is identical, except the bosses displayed are from NieR: Automata, rather than the original NIER.
I recognize some of them, but to my knowledge the only Humanoid Bosses I fought up to this stage have been 3 who are
Adam, Eve and 21O/21B.
There were a bunch of B Class Androids, but they were a side quest and I wouldn't call bosses, yet there appears to be 5 in the middle row (which I assume Adam and Eve are the ones on the far right)
So, who are the bosses shown in the Trophy Room?
Also, is there a relation to their colour being Gold or Silver? The Baby Forest King is on the bottom and is Silver, but it was never fought and the figure at the top right looks to be the boss that 2B fought in the Abandoned Factory during her escape, but in 9S's route, it was never fought.
Best Answer
Not all of the statues are technically bosses, as there were not enough bosses to fill in all of the spaces.
In order, from left to right, top to bottom, the "bosses" featured in the trophy room.
So-Shi
Auguste and Friedrich
Adam and Eve
Beauvoir
Additionally, on the floor is the Goliath Flier that appeared right before Grün made his appearance.
From what I've gathered, the colors of the statues mean nothing.