Get 10,000 points in Trial mode, then press Select at the Puzzle mode selection screen to change the background color.

Successfully complete the indicated task to unlock the corresponding bonus:

Chiccolor Background: Successfully complete 40 stages in Puzzle mode.
Flower Background: Successfully complete 20 stages in Puzzle mode.
Japan Background: Successfully complete 80 stages in Puzzle mode.
Street Background: Successfully complete 60 stages in Puzzle mode.
Kasuri Image: Successfully complete 30 stages in Puzzle mode.
Raydust Image: Successfully complete 50 stages in Puzzle mode.
Roller Image: Successfully complete 70 stages in Puzzle mode.
Music 4: Successfully complete up to Trial 3 in Trial mode.