“the old-wives’ notion that what a woman sees in pregnancy can affect her unborn child.”
old-wives’ notion?? The Mekor you gave is actually correct & this minhag has many mekoros.
Bli”n I will try to look them up for you but any of the frum pregnancy books should discuss it. Check there. Specifically “The halachos of pregnancy & chidbirth”. I don’t remember the Rav’s (author) name but he was a talmid of R’ Tuvia Goldstein Ztz”l.