I can't really tell from the picture. It could be stress. It could be her age, mine was about the size of a dime when I got her and didn't have great color, often she was almost transparent, I can't tell how big she is from the picture. Do you have a big enough tank for her? Since she is in QT and there are no other signs of a problems, I'd observe her closely for the next month, make sure the water quality is good, feed her high quality foods and plenty of plant based food like algae sheets. Be prepared to treat quickly if it becomes necessary. Otherwise, if you don't already have them, I'd make sure you have basic meds on hand.