Oh, come on. Shrek is green, and Fiona couldn't tell until he took off his helm, remember?
she also didnt find it odd a guy the size of a vovlo had the dexterity of gymnast
He was her valiant and gallant knight, who had come to save her and sweep her off her feet in an extravagantly romantic way. Of course he was tall and stalwart, and of course he was graceful and nimble.