Font color white (snow) on macOS Notes not visible on iOS Notes
TL;dr Do NOT choose white (snow) colored text in the Notes app on macOS while in dark mode. It cannot be seen in dark mode on iOS Notes.
I use macOS Notes a lot and figure out that if I allow the Notes app to set the font color by choosing "Body" or any other standard format from the Format menu, it shows up as white text on a black background when dark mode is chosen on iOS Notes. This is proper behavior.
Or, if I choose any color BUT white from the color picker (e.g. Lemon) it shows up properly as the chosen color on a black background when in dark mode on the iOS Notes app. This is proper behavior.
However, if I use the color picker to choose white (Snow) text on the Mac in dark mode I can see it just fine BUT on iOS Notes in dark mode it will become invisible. This might be considered a bug but I found complaints as far back as 6 years ago so apparently Apple does not plan to change this behavior.
The upshot is, if you want to have white text in dark mode work on both the Mac and iOS devices then use the standard formats for fonts from the Format menu in Notes as these work properly on both platforms.
Happy Day!
iPhone 13, iOS 18