There seems to be a few people who don't seem to like the colour change in the forest biome background, but honestly I don't see a problem with it.
While Having the brighter, cooler green would blend nicely with the foreground, let me take it the other way.
Sometimes, this game can strain my eyes when trying to take in what's happening to my character, or trying to tell what's collision and what's not. The subtle bit of contrast can be a big deal when it comes visibility.
On that note, I'd like to see some other changes to help with that in mind.
One of the most notable examples for me is the demon ruins in the Underworld. It is not very clear what is collision and what is not, due to the lack of contrast between the obsidian bricks and walls.