水色琉璃不发光
[shuĭ sè liú lí bù fā guāng]
'Shui Se Luli Bu Fa Guang', which is literally translated as 'Aquamarine colored glass does not emit light'. The aquamarine coloured glass here may indicate that it is valuable, but it does not show its luster by itself until it meets some circumstances - probably means that this person considers themselves unpretentious but beautiful