It's an interesting fantasy to paint such a fat ass green! Ladies with such an ass are especially good in the crawl position, a boner is assured. Except you have to have a decent length tool. If you don't have one, I recommend laying the lady on her back and fucking her with your hands on her thighs pressed up against her belly. Otherwise you can't get the dick in deep.
All logical: he takes off the brunette, she takes off his pants, and they are each engaged in their usual business. The girl, by the way, will go far in the modeling business, where the ability to completely swallow a big cock, while smiling at it, is highly valued. Give a deep blowjob with a friendly face, this is memorable and the next time you choose a model, she will automatically be at the top of the list!
I'd fuck her.