Is there any waty to change the color of closed days on calendar.

For example on CalendarImage1.png , back color of every days are white.
Customer want to change the back color of weekends and national holidays to red.

I know there is disable setting which reference the calendar rule, but customer said that sometime they need to select the weekends and national holidays too.They just want to change the color.

Is there any way to achieve this requirement?