rajrkodeep,

You will have to do this on the client side in javascript.  You will need to hook up the WebCalendarView's RenderDay event, and in that event check to see what day it is, and if it is a day you want to color, change the background.  The code will look something like the following:

function WebCalendarView1_RenderDay(oCalendarView, oEvent, day){
    if (day.day == 1 || day.day == 25) {
        day.element.style.background = "red";
    }
}

Hope this helps,

~Kim~