All eggs start out white, and the color is applied in the oviduct or shell gland. She could be suffering from impacted oviduct or salpingitis. She probably feels lousy when the egg products are in her egg tract. I would keep offering the calcium. Hopefully she will get better. Some vets will offer hormone implants to stop laying. Decreasing light and keeping them in a dark cage for 16 hours a day can eventually stop them from laying temporarily over several days. Hens will sometimes stop laying eggs after suffering laying problems.