These symptoms can be related to the arm injury
.The purple and black colour is because of the collection of blood below.If there is swelling there associated with redness
and local pain,then it could be due to local infection of tissues called as cellulitis
or there could be frank collection of pus there.Chances of wound infection
become high if your husband is diabetic.
If it is not so then the cause of fever is something else and then the cause has to be found out by proper blood investigations.You must consult your doctor tomorrow for proper local examination and investigations.In the mean time give Tylenol
to him and can be repeated after 6 hours.