Regulate your clothing so it doesn't become sweat soaked, use materials such as thermax or poly-pro which wick moisture away from your skin as you sweat, and wear a rainproof shell which sheds moisture and does not soak it up when it is precipitating. Always bring dry clothing with you to change immediately after you are through with a run or walk. When deciding what to wear for your run or walk, first check the temperature as well as the conditions outside. Running with bare legs, although very alluring and sexy in cold weather, is not advised. The red color of the skin shows that a great deal of the blood is detoured to the skin trying to keep the body warm and is not going to the exercising muscles where it is needed most.
Cold muscles feel tight and are more susceptible to injury, especially pulls and strains.
I suggest lycra tights or other leg covering when the temperature is below 40. Many options in materials for tights are available, from water resistant to extra warm fuzzy polypro that can be worn as the condition change. Fabrics that are waterproof, but can still breathe are best for external layers. Gortex works quite well if you don't sweat a great deal. Polypropylene is excellent next to the skin as it wicks away the water and allows a warm air layer to remain.