Mucous membrane colour is primarily determined by the red colour of oxygenated haemoglobin and the blood flow that takes it through the tissues so anything that changes the Hb concentration of the blood flow will affect the colour. How the colour is described may also depend upon the background colour of the mucous membrane (eg muddy or grey as opposed to white). It may also be affected by any other colours that may be mixed in with the red or by disease in the mucous membrane. Here’s a normal dog just to refresh your memories before we go on to abnormal.