To me 45 F would not be really cold but it would be chilly enough to make me shiver without wearing at least a light jacket.
45 F is also chilly enough to where I would turn the furnace on to take the chilly feeling out my house but 45 F would not be really cold.
Really cold weather to me where I would want a heavy coat would be 35 F or lower in temperature that's when I would really start shaking due to the cold and would want to bundle up really good before going outside.