Definitely to do with the reflective color, messing with the IR

Put a a piece of black duct tape on the roof,,,,you'll soon see some action !

Oilfield wise in desert - high heat locations all the pipework is painted silver to reflect the heat

mind you on the hot days even chrome still absorbs a lot of radiant heat.

In venezuela and Oman you'd often see us with buckets of water being used as tool holders !

Heat and heat transfer is a science in its self, in my field we don't use IR measurement for issues like you are seeing.

Standardly we'd use thermocouples or PT1000 sensors for measuring exterior temperatures

I sell design and install fiber optic temperature measurement systems for oilfiled and pipeline monitoring.

The tech is pretty interesting lay down a fiber anywhere you want and I'll tell you the temperature every 1.6ft along its length, up to 15KM from the measurement unit.

With nothing but light and a fiber, no sensors or detectors.

So I do and have similar issues in lots of jobs once we install and test.

1 job I had we had'nt even installed the fiber yet it was just on the roll, I had huge spiky data 60oC down to 15oC.

I thought the machine was busted, but it was just radient heat, early in the morning the drum was still cold underneath but hot on top from the sun, the bottom had'nt caught up with ambient temps and was still at night times temps

So I had a hot spike every time the cable hit the top of the reel and a cold spike every time it reached the bottom.

We had to wait 4 hours till the client would believe me !
we had to rotate the drum every 15 mins till temperatures evened out and he'd let us install the fiber