My new mammilaria not doing well

[SylverCloud]

Its just been 20 days that I got this Mammilaria (pic attached) from a plant exhibit. I potted the plant myself and it looked good then - mostly green with tinges of purple on tips. Its has now turned mostly purple and I see grey/white spots developing on areoles. Is that sunburn or a pest? I placed it on balcony wall. It is only exposed to morning sun and other times its only bright reflected sunlight.
Thanks.

[adetheproducer]

The red look like stress from sun move it to a shadier spot and gradually introduce to more light over a few weeks make sure you keep it the same orientation so the side that faces the sun does not change. I made a make shift shade screen out of a wire coat hanger and an old pair of my wifes tights. I layered it up several times so as the weeks go by I cut away an layer at a time so the shared decreases untill its in full sun.

[SylverCloud]

Can I move now move it to shade right away, or should this be done gradually too ?

[adetheproducer]

no get it in shade straight away or build that screen and pop it infront of the plant so the sun shines through it onto the cactus.