This guide is a simplified overview of all the changes in the World of Color Update (Java Edition 1.12.x releases), which assumes at least some familiarity with the Exploration Update (Java Edition 1.11.x releases).
Mobs
New
Name
Image
Habitat
Drops
Note
Illusioner
Can only spawn by using the /summon Illusioner
command
New Illager type
Affects players with Blindness for 20 seconds, then, he summons duplicates of himself
Parrot
Passive mob, tamable with seeds
Normally is flying around, but it sits, when tired
They're dancing, if a jukebox is playing music nearby
It is not good idea to feed parrots with cookies
Changed
Blocks
New
Name
Image
Obtaining
Tool Required
Uses
Concrete
Can be broken with any pickaxe
Can be used as a decorative block
Concrete powder
Can be broken with any tool or hand, but fastest with a shovel
Can be used as a decorative block
Can be turned into Concrete if it comes into contact with water
Glazed terracotta
Can be broken with any pickaxe
Can be used as a decorative block
Can be useful in redstone mechanisms, as blocks pushed by pistons don't stick to it on the side
Changed
Name
Image
Changed
Wools , banners and shulker boxes
Beds
Now, it is block and 3D model in the inventory
It has got 3D model as block too
It is available in color variants
Beds are made bouncy, though they do not completely reduce all fall damage
Hardened clay
Renamed to Terracotta
Buttons , levers , redstone torches , torches , and tripwire hooks
Fences , cobblestone walls , glass panes , and iron bars
Now connect to the back and underside of stairs
Items
New
Changed
Name
Image
Changed
Map
Non-mob entities
Changed
Sounds
New
Name
Trigger
Sound
Xylophone
It will be played, if Bone Block will be under the note block.
Bell
It will be played, if Block of Gold will be under the note block.
Flute
It will be played, if Clay will be under the note block.
Chime
It will be played, if Packed ice will be under the note block.
Guitar
It will be played, if Wool will be under the note block.
Parrot
Illusioner
Changed
Name
Changed
Fishing Rod
Eye of Ender
Throwing an eye of ender
An eye of ender exploding or popping back into item form
Putting ender eye in end portal frames (dinging sound)
End portal
Completing the end portal and having the portal spawn (evil sound)
Boat
Player
Player drowning
Player burning
Notifications
Completing a challenge advancement
Toast notifications
Gameplay
New
Name
Description
Recipe book
Catalogs recipes that are unlocked when the criteria are met
When a recipe is clicked, it will appear in the crafting grid, and can be crafted if materials are available
Changed
Name
Changed
Advancements
Replaces Achievements
Can be customized via JSON files
There are currently 5 tabs
Now, it can be open by keyboard keybinding L .
Other
Changed
Name
Changed
Java
Support for Java 6 and 7 was dropped in this version, so Java 8 or later is now required.