They made a comment in the podcast how red was the only colour we saw in his otherwise black and white world. That’d be enough to explain his attraction to Red for me, (though indeed, the booty shorts are probably explanation enough ;)), because we’ve now seen that the one thing he’d been obsessed with finding to make his experiment complete, was the perfect, glowing, red heart.
And when Regina met him for the first time, he was sketching a white rose or something.