Back to the painted cactus for a minute. They are real live living plants that have been somehow colored. Like the Phalaenopsis that show up in vivid colors every year holiday.
Costa Farms, the 'inventor' of Desert Gems Cacti are dyeing the spines. The ones in your photo are Mammillaria vetula ssp gracilis - Arizona Snowcap - but there are Opuntia (prickly pear) also. As the cactus bodies aren't dyed, the plants eventually grow out of the dyed part and become normal looking cactus again.
Other nurseries are spray painting barrel cactus. These plants can't photosynthesize and end up dead. And then there are all those cactus with strawflowers hot glued to their heads.
But consumers don't seem to mind because we live in a throw away world. How many orchids do you suppose get thrown out when they stop blooming?
Don't get me started. Oh wait, you already have.