Revise visual representations of "green" week and "red" week

[jbevis]

Currently the calendar view displays weeks as either green or red.

This creates numerous accessibility issues especially regarding red/green color blindness, specifically deuteranopia.
https://uxdesign.cc/color-blindness-in-user-interfaces-66c27331b858

Essentially a good chuck of users would be unable to discern difference in weeks.

Proposed solution: Remove green weeks altogether. Only change background color if going negative.