Recolor admin boolean field icons from green and red

[Matthew Nuzum]

Background
Some colors convey information. Red means stop, danger, needs attention. Green, when accompanying red, means go, good, everything is OK.

Problem
When using the list display in the Django admin, boolean fields by default are shown as a red circle with an "x" in it for False values, and a green "checkmark" for True. Because of the color and the icon choices, this makes the assumption that True is good and False is bad.

How to reproduce

1. Create a model that has a field for "note" and one for "Needs urgent attention"
2. Add a record such as: note: "London Bridge is falling down," Needs urgent attention: True.
3. Add a record such as: note: "I think we should have casual dress on Fridays", Needs urgent attention: False.

When you look at these, the casual dress note will have a red x, which conveys alarm, while the falling bridge will have a green checkmark, which conveys an acceptable state.

Expected behavior
True and false would be neutral. Having a visual indicator is fine, but it probably shouldn't be red for false. A checkmark for true is pretty common, so that should be OK, as should an x for false, which is common as well.

[Tim Graham]

A design decision like this needs to be made on the DevelopersMailingList. Please start a thread there. If there's consensus to change the icons, we can reopen the ticket.