Number 3 is a Gymno. Round spines without transverse ridges. These are prone to discoloration, and if they recover it can take years. Enjoy the color it is, as long as it is not soft, it doesn't seem to affect the plant. I had a similar one turn red, candy apple red because of the cold and it remains that way. Still blooms, etc. and even has offsets. This is a Noto with a similar problem, though not as discolored as your plant. Here's a Gymno with a rouge problem from the cold. It is this color all the time now. Offsets taken before the cold episode maintain the green color. The same plant can be seen in the back center as a greenish plant a year or 2 ago. I has a bloom sticking up, just to the right of the one with yellow flowers.

Leslie, seems you need a greenhouse. Save those pennies and in a few decades you can get a small one! Seriously, I know how it is to have too many plants to cart in and out, not to mention looking for space indoors for winter. So, I have whittled mine down to the lemon, three (for now!) bird of paradise, a few orchids and a handful of other tropicals. The lemon, birds of paradise and orchids go out for the summer. I used to have camellias and a gardenia, and some cacti, but I have relegated myself to growing only the ones of those three families that can stay out all winter. I have several camellias and cacti, and one gardenia. The camellias and gardenia have some browned/burnt leaves, but then we did have that one very cold snap where it got down to -9 degrees one night. That was the coldest here in 30 years, so a good test. The hardy camellias, gardenia and cacti are every bit as nice as the tender ones, even more so because they can really grow better than potted plants. Of course, I really don't (can't) carry all those heavy pots anymore anyway, but it's fine. The camellias are starting to bloom now. The cacti bloom in June/July, and the gardenia probably late July/August.

Well, it´s dead. But some plants in the same container seem to be doing OK, which have obviously had the same conditions. We can only really guess at the reason, could even be some obscure infection, or no real reason at all, but like other folks say, your soil does look a bit suspect. There are as many favourite soil mixes as there are growers, and I have now firmly settled on a well-draining gritty mix with a good proportion of limestone for my desert cacti, with just a little organic material. I totally avoid soggy peat, which means any commercial ´cactus mix´, as they are invariably full of peat or even worse - ´forest product´- read sawdust. A gritty mix in unglazed terra cotta pots will set you up. Err on the dry side rather than overwater - it is quite difficult to kill a cactus through underwatering. They are succulents - they will store water when it rains heavily, then be well able to survive drought conditions for weeks or even months.

I just got this one a couple of weeks ago. Can’t wait for the purple flowers. Try this link. http://www.llifle.com/Encyclopedia/CACTI/Family/Cactaceae/19998/Notocactus_uebelmannianus