a black stallion or possibly a yellow mare (idiom); don't judge by outward appearance
骊姬之乱驪姬之亂li2 ji1 zhi1 luan4
Li Ji Rebellion in 657-651 BC, where concubine Li Ji tried to throne her son but was eventually defeated by Duke Wen of Jin 晉文公|晋文公
骊山驪山li2 shan1
Mt Li near Xi'an with the tomb of the First Emperor
牝牡骊黄牝牡驪黃pin4 mu3 li2 huang2
a black stallion or possibly a yellow mare (idiom); don't judge by outward appearance
探骊得珠探驪得珠tan4 li2 de2 zhu1
to pluck a pearl from the black dragon (idiom, from Zhuangzi); fig. to pick out the salient points (from a tangled situation); to see through to the nub