The built in CalendarView widget doesn't expose the ability to change the color of the calendar cells in month view. See the source.
You might try the following approaches:
Extend from CalendarView and implement onDraw yourself. You'll have to reimplement all the existing drawing behavior, including these 4 methods:
protected void onDraw(Canvas canvas) { drawBackground(canvas); drawWeekNumbersAndDates(canvas); drawWeekSeparators(canvas); drawSelectedDateVerticalBars(canvas); }
Implement you own CalendarView that allows customizing cells. I suggest this project as a good place to get started, since it already supports custom cells.