Here is the full list of all 12 Black Rainbow Mystery achievements.
You've finished the game in Challenge mode!
You've finished the game without using any Hints!
You've finished the game (any mode except Challenge)!
Finish the game without skipping any dialog
Find 21 Special items
You've finished the game without using Skip (and solved all of the minigames)!
Find 14 Special items
Solve 10 Minigames without using Skip
Find 7 Special items
Solve 5 Minigames without using Skip
Find 1 Special item
You've solved 1 Minigame without using Skip!