This was done yesterday afternoon 5 pm with ALL of the rear doors facing the sun. The Ingot Silver was in the 113-114 range. Oxford White was in the 118-119, The others ranged in the 120s with the highest being 142 from the Carbonized Gray van. We do not have a Agate Black. The Race Red was 123.
Once the vehicle are heat soaked the temperatures will all be fairly close. The bigger issue with darker colors is when you are cooling the vehicle to temperatures lower than ambient. The greater light absorption of the darker colors will result in more heat gain that will need to be offset to cool down.
If an IR thermometer is being used to measure the temperature, it the measurements are most likely not accurate especially when comparing metallic and non metallic paints since the emissivity of those finishes will be quite different. I suspect that might be one reason why the white measured higher than the silver. The numbers posted are just a few random anecdotal data points. Feel free to misuse them to justify your aesthetic preferences.