Linking a Jewel Box with Charms of the same color will unlock it.
Every Jewel box has a number on top that specifies how many Charms of the same color need to be connected. The number decreases by one for each Charm in the link. When the number reaches 0, the Jewel box will open and reveal a Diamond.
The number on the Jewel Box can also be decreased through the explosions/Rays created by the Blasts or with the help of Birds.
In this game mode, it is not necessary to bring the Diamonds to the Necklace.