But there use to be more to it in pre-Windows 8. So, anything in Windows 7, 2000, XP, 98, and 95... There use to be an option called "Colors and Appearance", which looked like this:

That you would've been able to edit the actual windows backgrounds and text options, like you want.
The closest you can get now is what I sent you in the previous post.
There's also another option to take the Dark UI Scheme in Windows10 and apply it (which doesn't work for me).
It's not a SAI feature. Little Chiisai (the artist behind what you see on that image... and whom might be you?) only took a screenshot of PaintTool Sai and overlaid her pixel art on top of it. She's known pretty well for her pixel drawings/anime themes.