5 fckeditor on one page and background color

Hello. On my ASP .NET page I add 5 fckeditor and I have question how can I change the background color of fckeditor in whitch I enter a text ? For example I click on the 4th of fckeditor textbox and the background color automaticaly change from white to for example yellow. In fck_editorarea.css I can change body background color but this apply to all fckeditor's on page not only for active.