西瓜再圆也是甜的柠檬再黄也是酸的
[xī guā zài yuán yĕ shì tián de níng méng zài huáng yĕ shì suān de]
'A watermelon is sweet no matter how round, a lemon is sour no matter how yellow it is.' It signifies that true nature does not change regardless of superficial appearances; emphasizing intrinsic value or truth over appearance in a lighthearted tone using simple everyday elements.