like hui said colour of car effects the temp inside. Darker cars are hotter as they attract more heat while lighter colours reflect.

Also if you have no tints the car can be quite hot as well, so instead of respraying your car why dont u get some decent dark tints. (25% if you wanna stay legal or 10%-15% for ultimate cooling with good vision but is illegal)

That may help with the temperature problem

btw on the legality of tints. Police rarely bug you about it so yeah my old tints were like mirrors and most police won't give you a hard time about it unless your giving them one