I looked online and couldn't find an answer. I was told it means something similar to "poker face" here in Taiwan. Do you know what this might mean?
I guess the term you mentioned, yellow wife, is referred to "黃臉婆" (yellow-face wife).
"黃臉婆" describes a woman who has married for a long time. The (face) color indicates that she has aged with the burden of housework. (Someone says, in ancient China, to cover the aging face, women misuse the cosmetics with lead and make their face getting yellow. The elder, more yellow.)
It's a negative term. Husbands use this term to describe their wife as love is fading out. Wives complain the houseworks and the relationship by calling themselves as "黃臉婆"
I think there's some differences between poker face and this term. : )
黄脸婆 [huáng liǎn pó] 古代女性所用的化妆品落后，一般所用的搽脸粉含铅，有毒性，长期使用会导致脸色变黄。所以年纪愈大的女性，受害时间愈长，受害愈深。故年长一些的女性就会呈现“黄脸婆”的症状。 the ancient women's cosmetics backward, face powder containing lead, generally used for toxic, long-term use can lead to pale yellow. So the older women, the longer the time injured victims, more deep. The older women will show a 'Huanglian Po.'. 现代的“黄脸婆”
④指容貌不好看的女子，不一定是中年女子，带有贬义，一般是骂人时用的。 Modern 'wives' ①the older woman ovarian dysfunction, leading to endocrine disorders, melasma from forming on the skin, pale yellow. ② refers to women caused by aging of the skin surface, generating yellow melanin, cell deposition. ③The mean man of his wife's disparaging, often emotional problems, the man is tired of the woman, marriage crisis. ④The finger appearance woman is not good, is not necessarily the middle-aged woman, with a curse, is generally used