A few years back I sunburned the heck out of my Mendenhall 'Hildos.' Had in a south window on a ledge, and forgot to check the sunlight received as fall arrived and leaves fell off the bush in front of window. Resulted in two VERY scorched leaves that I still live with today. Ugh.
Fortunately, yours doesn't look nearly as bad as mine did. And I've also noticed fading of the marking on some leaves since then when I've left it in its summer place too long. It did regain some of the color after being in more appropriate lighting for a year.
Scoot it further away from the light source, and consider yourself lucky for catching it in a timely manner.