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]
The ancient women's cosmetics are backwards, with face powder containing lead, and those generally used are toxic, long-term use can lead to pale yellowness. So in older women, the longer the time of injury, the more severe. The older women will show a 'Huanglian Po'. 现代的“黄脸婆”
Older woman have ovarian dysfunction, leading to endocrine disorders, melasma forming on the skin, pale yellow.
Refers to women and is caused by aging of the skin surface, generating yellow melanin, cell deposition.
The mean man disparages his wife, often causing emotional problems; the man is tired of the woman, leading to a marriage crisis.
The appearance of women is not good, not necessarily for middle-aged woman, carrying negativity, is generally used.
All the answer mean 黄脸婆 yellow face wife. Normally would say it to Woman only.
- 黃臉婆 （Traditional chinese， which is writing in Taiwan)
- 黄脸婆（Simplified chinese， which is writing in China)
Poker face is
- 撲克臉（Traditional chinese), 扑克脸
As for traditional and simplified chinese, and why there look similar yet different. Please search relevant info.