In DkSII Archives we have come to the conclusion that Ancient and Everlasting Dragons are the same, once a Japanese Speaking person joined the ranks. Turns out their correct title is Ancient Never Ending (Everlasting) Dragons.
Also in a interview (god, I can't believe that's still not common knowledge yet) for shootaku (iirc), Miyazaki explained Gaping. He isn't a descendant of the Ancient Dragons, he IS an Ancient Dragon. Dragons are not living beings, they are more like moving forces of nature that change form to adapt to their surroundings. Seath grew tentacles so he could seethe more. Gaping turned into a huge mouth, because the thing he loved to do the most was eating. And Kalameet turned into obsidian and one eyes, because... /discuss
Also, I hate to make literal translations, so I try to go for the real meaning of a word. You say Kala can mean either Black or Time. I have three theories based on the meaning.
Lets consider the meaning of Time, from Shiva. I believe someone said "the eternal Time". Maybe the Kala here was meant to mean Eternity. Friend of Eternity; given Anor Londo couldn't kill it, so he would last forever.
Now, the one I'm particulary fond of; Black. In many languages Black and Dark are the same world (dark skin / black people - I use that as an example, because the game was originally called Dark Race, but later changed due to racism being a thing). What if they meant Friend of the Dark? Kalameet is in Oolacile afterall, using Dark Fire, making Gwyn be afraid to dispatch an army there, because after all, even Anor Londo dared not to challenge mighty Kalameet. Gwyn is left only with the option of sending his elite knights for a commando mission. They were to go there, kill Manus, all under the radar of Kalameet. We could go even farther, to say Gwyn, the White, had his White Dragon, while Manus, the Dark Lord, had his Black Dragon.
Lastly, the third theory I personally don't believe. Kalameet is friends with Velka, and is helping her acchieve something there.