I immediately googled "nipples on book covers" and learned that they "aren't done", that Amazon might not approve, but that "Germans love nipples on book covers".
But I also realized that the image was perfect. It contradicts the popular trope that "unisex" anything results in the erasure of differences. (Oh, really?) Sometimes yes, and sometimes no. Ungendered, genderfree, androgynous, neutral, genderbending, gender creative, nonbinary: they all look different on different bodies. The thong bathing suit (also designed by Gernreich) was originally intended to be unisex. Think about that the next time someone worries that unisex will make it impossible to "tell the boys from the girls".
So yes, the book has nipples. Brustwarzen. Telillas. Capezzoli. How very unisex.