This bunny cactus has been turning a bit yellow around the edges, as well having these white, shallowed areas or "cracks" like the one you can see in the center of the right pad. What's wrong with it?
It was getting a few hours of morning sun, followed by 2-3 hours of shade from the afternoon sun by the porch bannister and pillar, followed by a more few hours of afternoon sun. I took it back inside when I thought it was sunburn, but that didn't seem to harsh to me.
You may indeed have the symptoms of the plant being moved from a "protected environment" to the outside conditions. I do not know, where you live and what your climate is. At least here in the Chihuahuan Desert, cacti will sometimes be killed within hours, after they have been exposed to our merciless sun. So, if you had been growing your Opuntia microdasys var. albispina indoors, especially the afternoon sun could cause sunburn and the accompanying discoloration. This will be most visible at the edges of the pads (cladodes) and affect the parts more, that are not totally vertical.
Young growth will be more impacted than old growth. So, at first, it is a good idea, to either use a device that offers some shade over your plant or to place your cactus underneath a tree, so it will receive only filtered light. The least damaging sunlight is that, which the plant is exposed to during the morning hours. From late morning until late afternoon the sun's potential damage will be more severe.
Also, keep in mind, that because of wind, the pot holding your cactus will dry out faster, than if it were indoors. So, in addition to sunburn, you are more likely to subject your plant to dehydration, resulting in drought damage.
