What is the difference between Black-and-white Dreams and Colorful Dreams?

Black-and-white Dreams are the Dreams that have been credited to your account, but cannot be reddemed for bookings yet. To turn your Black-and-white Dreams into colourful ones, your balance should once have as many as 1,500 Dreams. As soon as it happens, all Dreams that have been accrued on your account become colorful, as well as all new Dreams that you will receive in the future.

Colorful Dreams are the Dreams that can be used for payment.