M. saetigera and pink nipples

I have this lovely M saetigera and it has had these pink nipples as long as I have had it, in winter storage and now in the 80s. I see nothing in the literature that says this is a common detail. Is it a sign of disease? What's going on?

It's probably caused by a lot of sunshine, but it is not scorched. Lots of cacti colour up like that in the summer. If it alarms you then try keeping it in a more shaded position.

Humm, I will investigate that. Thanks for your response.