Here’s Jane Birkin in the 70’s, knotting up her white tee and baring flat abs:

Jane Birkin The Style Evolution of the White Tee Shirt

And possibly most famously from that time period, Jacqueline Bisset steamed up the joint in her soaking wet white tee:

Jacqueline Bisset The Style Evolution of the White Tee Shirt

The end of the seventies is when the white tee began to take a more womanly shape, offering shirts with thinner fabrics, smaller shoulder areas and scoop necks.