They look fine, to me! They look like the undersides of many of my hoyas; dings, dirt, and misc. If it bothers you, try soaking the leaves for 5 minutes or so, in warm water. Then, get a soft cloth and wipe each leaf down on both sides. Keep in mind, they will probably just get dirty again! Life of plants!

Thank you. I was concerned that it may be due to frost damage and they may die and fall off. I'm so glad that's not the case.