That would be a good test.
I don't have any scientific measurements or proof to dispute that, but below is my personal experience.
I have 4 cars currently at my house, car 1 is model 3, car 2 has a steel roof with a glass sunroof and a retractable mesh shade, car 3 has a black steel roof, car 4 a white steel roof. Driving in the middle of a hot day, I can clearly feel the most amount of heat from the model 3's roof, whether it means higher cabin temperature or not I am not sure. In car 2, I only notice the heat under the glass sunroof, not other part of the roof. When I drive the model 3 and car 2 in summer, I often have to point the air conditioning towards the roof to be more comfortable. I don't feel any heat from the roof in car 3 and 4, those 2 with the full steel roofs. It is not because I can see the sun coming through the glass roof and therefore I feel the heat more. I don't notice the sun through the roof, and I wear sunglasses when I drive.
I have to say though my model 3's untinted windows seem to be have better heat rejection than my other car with no window tinting.