If you are designing all of this with Pega sections, then the color can be easily changed in the skin. No need to hand code HTML.
But if I misunderstood your question, can you please elaborate and send a mockup of your setup.
I just need to know Is it possible to add html code ? and If yes,What are the steps to do?Let me give an another scenario. There is a mock up screen.At top "WELCOME TO PEGA" need to move from left to right.I can make this using marquee in html.So I need to know where to add html code?