[IYAS9YAS]

I have a light colored Mazda 5 which has a large, sloping front window, and it seems to be hotter inside than other cars I have owned.

Yes, windows are the biggest factor. However, all things being equal, both light and dark vehicles, of the same make and model, will heat to the same point.

The fact is, the interior of a car can get well over 100 degrees in the summer, regardless of exterior color. At this point, as was noted in an earlier post, the A/C is coming on, and likely staying on.

[palmer]

all things being equal, both light and dark vehicles, of the same make and model, will heat to the same point

...if both are parked in the shade.