Chronic "Bacteremia" (often called "blood poisoning" - a misnomer) due to a bacterial infection can cause the veins to "redden" visibly. As the infection worsens, the visable reddening may spread to a wider area (Ascending Lymphangitis). Such instances are a SERIOUS MEDICAL EMERGENCY and must be treated quickly.
http://www.davidlnelson.md/Infection1_ascending_lymph.htm