eric wrote[...]it's difficult to see the difference between white and bold white[...]
[...]i don't know if the choice of replacing the number (on a menu) by the first word of the sentence is a good idea or not[...]
# 1 this is an issue which I have seen in X as well
and does not happen in tty console since the default non-bold white is a medium grey there. A workaround could be to use bold black for inactive content which also is a darker grey. Must be evaluated carefully though. If you wanted to test this real quick it would suffice to set screen_color to (BLACK,BLACK,ON) instead. Don't be scared by the looks of the variable and see for yourself :)
Telling from the background color and the pixel rendering of that screenshot I assume you are showing this from inside live JWM? I could make a color profile for you to include into the live JWM terminal to resemble the upper most screenshot of post # 1 which has very nice contrast.
While testing I see that you're quite right with the contrast even in tty, but the real culprit here is the separation of one single line in <tag> and <item> and only <tag> being highlighted. I suppose you did this to preserve the [variable] color of green for it would become white while being selected. Would that be such a big issue? I'll look further into this.
# 2 not a good idea. Just use --no-tags and make the whole sentence be a single <item> attribute or you'll heavily interrupt legibility. In you screenshot only the <tag> element is bold, why? The .dialogrc should actually make the selected <item> element bold as well to begin with.
Oops found it. Please change .dialogrc line 90 from:
item_selected_color = screen_color
to
item_selected_color =
button_active_color
Everything else: I'll make a test run later, sounds great. Fungal will probably be faster ;P
With the given (and corrected [line 90...]) .dialogrc its just a matter of playing around with three variables (TRON anybody? :D):

screen_color = (WHITE,BLACK,ON) <- will be all default text not selected including messages and inner borders
border_color = (WHITE,BLACK,ON) <- will be the outer border of course
button_active_color = (CYAN,BLACK,ON) <- dictates all selected elements
With this theme just make sure that the contrast between screen_color (inactive) and button_active_color (active) is good enough as you mentioned and try not to have the eye get focus on the border too much.
Functionality observations
- Cancel buttons appear to always throw the user back to mainMenu() - would be better UX to go the menu from before
- If I choose to have a separate swap partition I can enter the whole disk size and still get to the next step which should not be the case.
You may argue that one can not be stupid enough to do this in a real situation hahaha,...maybe could do a test for if rest is >= 5G for root to be possible to install, or just let it be :D (probably the better thing to do for now)
- I chose XFS for root and BTRFS for /home (yeah I know...) and the script bailed out with:
parted: invalid token: vfat
Error: Expecting a file system type.
(Now tested with various, seems to not be related to a specific FS, probably a spelling mistake in the parted command?)
Further playing shows that this is inside of some UEFI parted command only. The BIOS path seems to partition fine