htc one m8 screen colors and heat problem !!!

i have been using my htc m8 for about a year but recently after using youtube for while or whatsapp .. the shadow of app icons still appear on the screen sides and the temperature of the phone rise up .... then after a while the phone's heat gets down and these annoying shadow disappear . the performance of the phone still good .. i tried to delete big files but the problem still appear .. please help me ... 😃