What does "yellow face wife" (黄脸婆) 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. : )