1. You should be able to modify the background color and inner HTML using BeforeHeaderRender event handler (look for e.BackgroundColor and e.InnerHTML).
3. You should be able to activate the header using BeforeHeaderRender as well. Example:
e.InnerHTML = String.Format("<a href='javascript:dpc1.refreshCallBack(new Date(\"{0}\"), 1)'
title='Go to day'>{1}</a>", JsDate.FormatDateTime(e.Date), e.InnerHTML);