I have worked with at least twenty mothers who had blanching of nipples
accompanied by extreme pain of breast and nipple.   In one case, while the
mother fed her baby, I watched the other nipple turned dead white.  In  almost all these
cases, better positioning helped as did keeping the breasts/nipples from becoming
cold.   These mothers found that a sudden draft or cooling would
also cause the nipples to blanch and the pain to recur.   Warm compresses
were also helpful to some of these mothers.   I don't know if
thrush is the problem but it might be a possibility.
Interestingly, an old guide on breastfeeding for aboriginal women
recommends that they ALWAYS keep their breasts warm.
Eileen Shea, BSc, IBCLC