Black on gray vs. white on gray definitely seems like more contrast to me.
Yes, for some window elements, but at least for me, I don't see a black outline replacing a white outline around sidebar list text as introducing more contrast, at least as I understand the term. I've been seeing it as adding a visual element that's distracting since it doesn't seem necessary, for the user, to differentiate the area of the list text as much as this line does. It seems to needlessly add a second outline around most of the list text that it encloses, when the outline around the entire window itself that all of this is located on, plus the line between the list text and the body of the window, to its right, seems to be enough, at least for me, especially considering that the outline around the entire window gets nicely thicker when "Increase contrast" is on. Adding the cartouche line creates two parallel lines next to each other to the left, top, and bottom of the list text, making the extra cartouche line seem redundant on those sides, and even quaint and retro:
Maybe all we need is to stick with the nice clean look of a line only between the list text and the body of the window, to its right, as in macOS 15 Sequoia and prior versions:
The only way I can get close to this look again, when using Tahoe, is to turn off "Increase contrast", which has side effects I don't want, including removing the line dividing the sidebar list text from the items to its right. Tahoe's cartouche around groupings of controls, whether buttons or lists, is an iOS, iPadOS, and visionOS graphical thing, but it seems out of place in macOS's Finder and System Settings windows, since unlike in those other OSs (because they don't have "legacy" windows quite like these), it produces a double-line effect by placing a rounded rectangle within and close to the left end of another rounded rectangle, and especially when you see it only when you select the non-default setting of "Increase contrast".
My first image, of a macOS 26/Tahoe Finder window, shows another of my little peeves: there are now two pathname entries shown at the top of each Finder window, with the upper one being truncated since it's inline with the Toolbar items. This is the way it's been for several macOS releases. But this truncated pathname entry now becomes redundant since the fuller pathname is now shown just below it, so if the redundant upper pathname entry were removed, there would be more space for Toolbar items. The new longer pathname entry at the top of Finder windows also seems to make the Path Bar near the bottom of Finder windows redundant, or vice versa.
As I continue to play with the "Increase contrast" toggle in Tahoe, going back and forth with it, I can see how the cartouche is one way to successfully differentiate (or over-differentiate) the list text from the rest of the window it's in, and also from things (other windows, etc.) behind the window that the outlined list text appears in. But instead of changing the list-enclosing line from white to black, I'd like to see other approaches, even user-controllable options, like changing the background behind the list text to a slightly darker shade of gray, though maybe this would interfere with readability of the list text, or a light color, which might not reduce text readability.
I'm sure Apple has thought most of this through, and found that adding the cartouche line is a simple way of doing the job without adding extra issues like black text on a slightly dark gray or color-tinted background, without going down the rabbit hole of too many user-selectable theming options that might be confusing. But maybe giving us a choice by adding at least one or two more user-customizable contrast options to the overall interface, or even just Finder windows, would be nice.
