The colors on the ring of the top of the logs doesn't match the colors on the side of the log
For oak the ring is darker
For spruce it is lighter
For acacia some pixels are darker
For jungle it uses the same color palette but uses the colors that are too different from each other
While birch isn't pictured some of the pixels are slightly discolored
No clue how far back this goes, it likely goes back to 1.14
This isn't a bug and works as intended. The colors were changed slightly in order to make the outer layer of bark blend in more, to not make it stick out as much and to offer a better contrast and make it look more natural.