Android 4.x (including 4.4 KitKat) the dark mode you're talking about was the default look, and dated back to the really early days (to Cupcake, or 1.x). It only became white on the Verizon variant of the Galaxy S4 and S5 when they updated to KitKat (S4, the S5 shipped with 4.4 KitKat) and only on the settings menu or certain OEM apps. It became standard across the board after 5.0 Lollipop, either on a new device (such as the Galaxy S6, Note 4, Nexus 6, etc) or via an update to the OS.
The dark look was known as Holo UX, which was done by Matias Duarte, which should be a familiar name to anyone who followed the WebOS era (he was the UI designer behind it). It started on tablets with version 3.0 Honeycomb, and bled to phones via 4.0 Ice Cream Sandwhich through early KitKat. It was a sorta flat UI design, but kept relevant skeuomorphic cues, such as button textures and shapes, the darker theme, many icons still keeping skeuo looks such as the holo Google apps, and many third party apps. It changed the icons in the notification area from the green hue of Gingerbread to an electric blue. Samsung devices, thankfully since my eyes were a bit sensitive to neon blue, kept the Gingerbread greens.
Holo UX was when apps started getting hamburger menus, redundant settings icons (three dots, gear icons, and ellipsis in the same app) and gesture controls that took getting used to (YouTube, for example, when you'd hit the back key would always leave the playing video and go back to the search, whereas the Holo version would minimize the video which kept playing and display the search behind it, which I found very annoying).
But what came after in 5.0 Lollipop was Material Design, which was when colored text replaced buttons, when white became default background colors, and when icons became cartoons. It was Android's iOS 7 and came a year after iOS 7, in 2014.
Now they call it Material Design 2.x and it's even worse than the first time. It adds in rounded corners and a lot of other Apple-inspired change which makes Android look more and more like iOS to the untrained. All this talk of 'skeuomorphism coming back' is just referring to Material Design, which is still quite flat. Windows 10 is trending a tad towards skeuo but it's still in transition thus far. I'm hopeful that MSN Premium is a sign of things to come. Not sure how that will pan out. I guess whenever apps stop looking like line-art and text with retina-searing white everywhere, I'll be even more hopeful. I'd love to see us at least go back to Holo design, which was at least consistent, and combined flat UI design with relevant skeuo design. It was more, balanced, to say the least. Also, Google didn't change the guidelines for Holo every few hours like they do with Material Design.
The Samsung Galaxy S Captivate was a variant of the Samsung Galaxy SII. It was the first to introduce TouchWiz as a UI, but it was the Galaxy SIII, the successor to the SII, which introduced the Nature UX variant of TouchWiz, which still remains my ultimate favorite phone and UI. I got a SIII still active as a backup mobile line, as well. Nature UX combined skeuomorphism with elements of nature, such as wallpapers, colors, app UI design (such as the weather widget, alarm widget on the S4, lockscreen animations such as the water effect on the SIII) and sound effects (alarm tone "Walk through the Forest", locking and unlocking water sounds, touch droplet sound, charging sounds, and various other tones). It was combining two things I adore to this day. Whatever Samsung has become recently, sadly, is so different from the 'eco-centric' approach of 2012-2014, and doesn't interest me at all. It's too different, too far from what I find comfortable, and yes, they got beautiful hardware, and yes, it's lovely until the screen turns on. I still cling to the belief that voice controlled things like Bixby and Google Assistant are intended to be mere workarounds to the ugly UI design of "One UI" (what a boring name too).
