Indigo in her hosiery

"indigo in her hosiery" from a puritan in babylon the story of calvin coolidge
by william allen white.

I haven't read this book, but I think it might possibly turn out that White was talking about some intellectual female, or what was then called a bluestocking. Indigo is a blue dye, which I suppose could be used to dye hosiery. Bluestocking, as an epithet for intellectual female, has its own history. Look it up.
SS