We like layering whites when all pieces involved could be worn on their own. Not that you have to, but you could. A tank, a tee, a dress. A guideline (we don't like rules) that comes in handy when layering white over colors as well.
If the under thing happens to be a lingerie thing (a slip, a bra, a body shaper) then our preference is for nude.
Camis cross into both categories, so we recommend choosing whatever color, or lack of color, feels right for you!
Nude Cami from Shirtini's Under Things Collection
White Cami from Shirtini's Under Things Collection