烟花绽放过后只剩黑暗彩虹绚烂过后之剩空白
[yān huā zhàn fàng guò hòu zhĭ shèng hēi àn căi hóng xuàn làn guò hòu zhī shèng kōng bái]
It implies the transient nature of beauty or happiness – fireworks and rainbows are brilliant when present but leave darkness or emptiness in their wake, like fleeting joys in life.