Thank you for your query.
Mottling of the skin can be seen in fever
if the temperatur rises fast. At that point the core body temperature is raised while the peripheries are cold
. Once the child is covered and the temperature of the peripheries rise the mottling disappears.
As your son is having cough
and fever for two days now I suggest that you get him examined by a doctor to rule out any other cause for the fever.
I hope I have answered your query to your satisfaction.
Wishing your son an early recovery.