Rubor in inflammation is due to-

four cardinal signs of inflammation: rubor (redness), tumor (swelling), calor (heat), and dolor (pain). A fifth clinical sign, loss of function (functio laesa), was added later The vascular and cellular reactions account for the signs and symptoms of the inflammatory response increased vascular permeability leading to the accumulation of extravascular fluid rich in plasma proteins, known as edema The redness (rubor), warmth (calor), and swelling (tumor) of acute inflammation are caused by the increased blood flow pain due to the release of chemicals such as bradykinin and histamine ref robbins 9th ed page 93