Temperature rise is about 25% higher for the black car.
I think you mean 9%.
I’m not too surprised to see a difference. But I always found that the interior color had a lot more to do with interior temps. I’ve owned white interiors and black interiors…and the white interiors always seemed a little cooler.
umm… percentage change for a temperature reading is quite meaningless. If you don’t believe this, change the temps to C and recalculate the percent, it will be different.
sorry…
Nope, temperature rise is 25% higher. Outside was 85F, inside was 104.4 F (about 20F rise) and 110 F (25F rise), so the black car had a 25% larger change in temperature compared to the ambient. Same would be true in degrees C.
delete
Nope, temperature rise is 25% higher. Outside was 85F, inside was 104.4 F
OK…I thought you were talking about the difference between the white car and black car.
Change those to ºC and you get 29.4ºC and 40.2ºC
and the percentage change is 36%
Which is why I say percent changes in temperature only make sense if the temperatures are in K or R, absolute.
I guess the point was that the black car temp was 110 and the white car was 104 so a difference of 6 degrees. So the black car was 5.7% hotter than the white car. What relevance does the outside temp have to do with it? A 6% difference is no big deal in my view and would much rather have a dark car with a dark interior-especially when its 10 below out, where a 6% difference might help a little before the seat heaters warm up.
No, the percent rise in temperature remains the same. 20F becomes 11.1C, 25F becomes 13.9C, so the 2.8C rise/11.1C is still 25%.
BillRussell is correct. You can only calculate a meaningful percentage difference for a scale that’s 0 at absolute zero.
If you don’t believe me, picture repeating this experiment in Minnesota in January. If the white car ends up at 0 F and the black car ends up at 10 F, would you claim that the black car is infinitely hotter than the white one? If the white car ends up at -5 F and the black car ends up at 5 F, what would you claim the percentage to be in that case?
Nope. I’m only looking at the change in temperature from ambient. That’s the whole question, right? Which color car heats up more (from ambient)? When you’re looking at temperature changes (not absolute temperatures) it doesn’t matter which you use, F or C. Honest!
In your first example, it depends what the outdoor temp was. Assume it was -10F, then the white car heated up 10F and the black car heated up 20F, or 100% more than the white car.
I like absolute,the farenheit scale, really only has relevance for a living creature IMO
Yes, the change in temp is what you want. The change in percent is meaningless.
Another example. Temp started at 0ºF and changed to 10ºF. That calculates to an infinite percentage change. Does that mean anything? no.
edit, just realized I’m repeating lion9car’s statement.
Not sure I’m being clear. The % value is to compare the temp change for the white car to the temp change for the black car. In your latest example, if they both started at 0F and ended up at 10F, then there is 0% difference between the 10F change for each.
kmccune: the Fahrenheit scale is NOT absolute. Only the Kelvin and Rankin scales are absolute.
Not enough difference to make me NOT buy a black car again.
The reason I DON’T ?..no RED interiors anymore.
79 chevy pickup.Black/red…still have it.
had black /red 78 Cordoba and 92 Explorer .
Had a white/red 80 Bronco and a tan/tan 91 Explorer along in there too.
Now have silver/grey 08 Expedition and red/grey 06 Escape hybrid.
— still like black/red the best .
and the temp differences are a mute point as BOTH are dang hot till you turn on the A/C.
I might raise a couple of points about the testing. You’re using one thermometer which is being swapped back and forth with short time intervals. This means constant opening and closing of doors, possibly air currents having an effect on one or the other, etc.
Wouldn’t a better method be to use 2 thermometers verified accurate to each other and never open the doors during testing?
Another point and I bring this up from my climatologist son. Some of the global warming stats are being skewed because of this I might add. In the climate world the proper temp testing means the thermometer has to be located so many meters above the ground and so many meters away from any building, car, junk pile, or whatever and out of direct sunlight.
You have a dark car parked next to a white one. The white one reflects heat which the black one absorbs so that could explain at least some of temperature differential.
This would be similar to flawed climate testing where for example a thermometer was located near some junk cars and catching the glare off of the windshields or another which was located near a building where it caught the glare from plate glass.
Just some food for thought… 
That reminds me of the skyscraper that melted parts of a Jaguar:
So I admitted defeat, it was a white elephant bet, something from my mother in laws stuff we got vs got vs something from his father he got. He was really happy with the high relief German Beer stein, put it in the cabinet after a few trials of course. I remember seeing pictures of nomads in the desert with black garb, and also white garb. I was not sure how it was going to turn out. Less stuff I am happy, he is happy.
And you furthered the great cause of Science. Well done. 
All of this leaves me with one thought…
Butterscotch. Butterscotch leather is as beautiful as it gets.