with most car temp sensors, you need to drive a little to get the actual temp because of it sitting in the heat. Now, black or dark cars will be hotter but it might not directly effect the Temp sense. if it is not close to the paint. Another thought: I am an HVAC technician and thats what i do for a living. In my town (grand Junction, CO) the temperature varies at diiferent areas of the city and i mean by a lot. I can be in one area measuring say 99.9F and then 10 minutes in another place measuring 106F and then again somewhere else measuring 103.5F. I take measurements all day long at each job i come to to measure A/C System's superheat and charge systems correctly. If you temp sensor is 5-6 degrees off, don't worry because it is probably right, just drive for a while to see if it stabalizes and it may be right or may go down or up. Another thing to consider is where the News station you listen too gets there Temp info because it is in a different area as well. On average, the NOAA weather station here is about 6-8 degrees colder then i read consistenly. In the summer when they are getting 104F, i might get 111F. In the winter when they are reading 4F i might get 12F.
TO summerize: it all depends on location and how long your car is setting can also be a variable.
p.s.i also get around 6-20F hotter then outside ambient on rooftops depending on the roof color and outside temp. Food for thought.