Overdue by -10 which means overdue by 10 minutes. How do i swap the '-10' to overdue by 10 minutes using case when in sql?

Question

CASE WHEN Color LIKE \'%RED%\' THEN (10 - (DATEDIFF(MINUTE,Calltime,GETDATE()))) sometimes might give a -10 value. My question is when i get a value <0, how can I change