Although those dark colds have a title cinnamon on them there not a cinnamon theme at all, I had to download the things to see for myself, if you notice there all metacity themes, every single last one of them, with duplicates in the cinnmaon folder of the ones in the other folders, none of these are cinnamon themes at all, a cinnamon theme should be in a cinnamon folder, they don't need an index.theme file only the gtk and metacity files do. And I might be wrong they must of changed things around, I just tried it without the index.theme for the gtk and metacity and it showed hmmm it's been too long since I made one I guess lol.
So yup it should show up it did in mine. Wow wonder when that happened I been away too long
Anyhow this is how it works now
lets start this over again.
The theme has to have a main folder with the name of the theme on it, then within that first folder has to be either the metacity, the gtk or the cinnamon or the xfce or all of them at once, looks like the ole index.theme file is passe now (good riddens to it, just an added headache anyhow), if you look in that dark cold main folder you will notice it has a cinnamon-muffin folder and a metacity folder within each are three more folders, one set needs to be put in the .theme folder to show up (if you go in each you will see a metacity folder), you only need either the three that are in the metacity folder or the three that are in the muffin folder, do not place both because they have the same name.
wow this is sounding confusing to me lol sorry about this I'm riding on no sleep.
To make this clearer and because I'm dog tired here is an image to help explain it better.
I have a theme I made called SteampunkLinux within that folder you have you other folders like so.
I took away the index.theme that would normally go in here also and it shows up fine.
The darkcloud one you have is this.
notice it has two folders but this will not show up in the themes why? because within each of these are this:
Then within each of those you have a metacity file
The theme reads the first layer from the lead folder (main named theme folder) then it looks for a gtk, cinnamon, metacity,xfce,unity, folder etc from there then it only goes one more layer deep, if it goes into the metacity folder and doesn't see a metacity.xml it wont show up, same goes with the rest, it looks for the gtkrc file or the cinnamon.css etc. Does it hurt to have to a index.theme file? not that I see or know, but looks like we really don't need it anymore, thanks for getting me to look into this or I wouldn't of realized it things changed while I was gone either lol.
So to get all those dark cloud metacity files to show up just copy paste or drag the folders DarkCold4 DarkCold5 and DarkCold-First into the .themes folder and they should show up, sorry about the confusion, been away to long, and I need sleep lol.
Hope I didn't make this too confusing, and if you like an animated login screen I made 4 so far (mdm) but you have to have the new mdm installed to make them work, you can check them out on the deviantart site, I think Clem is adding the new mdm to the next linuxmint so no installement will be needed, not sure about this but i think so, but it can be added now, just some more eye candy for the login screen
all my crap is here: lol samriggs.deviantart.com
Have a good one I'm off to get finally get some sleep