Hi S.Gangireddy,
For the month view of canlendar, you can debug at following method. There is no standard customzing to change color. So you need to change the coding and css files correspondingly.
CL_CHTMLB_CALENDAR_MONTH
Method RENDER_CELL_BODY
CL_CHTMLB_CALENDAR_MONTH
METHOD RENDER_CALENDAR_BODY
Best Regards,
Bruce