https://prnt.sc/vh7d45
Color for titel should not be used for textfield.
foreground should be always black.

Do you mean the note text? Text and title have separate color selectors. (The one for the text is at the bottom next to the fonts dropdown)

I mean the text with the red underline in screenshot, thought this was obvious ;-)
you can hardly read this text, it should always be black.

I intentionally did it this way, because it's more intuitive. Otherwise you click a color and nothing changes, so you don't know if the color button is for title, text or both.

I could make the background darker?

if it works, then it's ok, it should be readable with any selectable color.
So black would have been the easiest to implement) (I am a lazy developer) ;-)
In real world I would not expect that the foreground color of a editable textbox changes.