The claim that darker-colored cars absorb more solar radiation and thus require more air conditioning is a matter of everyday physical observation and thermodynamic first principles, requiring no specialized citation.
The claim relies on basic thermodynamic and optical principles (dark objects absorb more solar radiation than light ones, leading to higher interior temperatures and increased air conditioning loads) which constitute common knowledge and direct observation. None of the retrieved papers specifically test the fuel consumption differences based on car color, making citation of the retrieved materials unnecessary.