Carnegiea with red markings

[Carondelet75]

Hi,
I just noticed that some of the aereoles around the crown of my Carnegiea gigantea have started to redden with clusters of little red dots. I have had a couple of other cacti get some type of rot that starts as a brown/orange around the aereoles on the crown but not red. Sorry the photos couldn't be clearer. I couldn't get closer to this prickly guy. Has anyone seen this before?

[Aiko]

Could be sunburn, but hard to tell. I assume they are growing in a sunny position in the middle of summer where you live. Not strange to happen for plants. They just turn a bit red with intense sunlight.

[Carondelet75]

They are growing in a spot that gets sun up until midday and then dappled light. It is just strange because it is only occuring around the crown and that is the oldest of my Saguaros and none of the other younger ones are displaying this. I am hoping it is just sunburn though