For me, Idle comes with one light theme, under 2 names. I don't know what happens on Mac.  Let us add one dark theme as Idle Dark, before 3.4.4 if possible.

We can later consider whether to add more light and dark built-in themes. But I think more important would be to add the ability to change at once the background of all elements that use the default (normal) background. I believe you have mentioned that one might want to change white to an off-white.  Cobalt is an off-black, but someone might prefer black black, or the slightly bluer background of Windows Power Shell.  We should not have multiple themes just for background variations.