My oldest rat was like that when we first got her, except she would get pretty snippy when I tried to hold her, then again - she was pregnant and I had NO idea. Definitely a huge surprise a few days later, but she eventually warmed up to us when the babies got older, no sooner though!
You're right! she does have those markings because she is half double rex and half hairless

Her dad, Brutus, was the double rex and his marking were just like hers but he was covered in almost a thick like fuzz and his head still had long fur :) Disney, her mama is a hairless dumbo and looks a lot like dude, same color and ears

she's a perfect mix.
Love my ratties though, most people are very shocked when I tell them I have 5 but they make awesome pets.