What Causes Swelling And Discolouration In Legs Of Person With Low Blood Pressure?

My father is 93, admitted recently to hospital due to a number of falls in 48 hours. This seemed to be due to low blood pressure and giddiness on getting up, so he tried to stay in bed a lot of the time. Consequently, his feet became swollen, over the last three days moving up to his knees. One leg in particular is shiney, hard, swollen and a slightly different colour to the other leg, e.g. yellowy/greenish. He has an underlying possibly CMML - not confirmed due to refusing the bone marrow test. Any ideas.