I originally thought that it was a sim and more specifically Bebe Hart since it looks like a yellow top with purple bottoms and brown hair, but the brown is the same color as the theathre rabbithole, so. And now it seems like the hair might be actually black or grey. The other colors are propably also not the same.

It might not be a sim it might just be part of the painting, as in this was painted\rendered and it's just a few blotches of paint so they could pick those colors and put them somewhere else. Or it could be shadows from objects, but the shadows aren't there in-game. Maybe something that was flying by, and I'm just projecting an humanoid image.

So it's either a puddingface that was sitting on the bench as the photo was shot and then changed with filters, a wild stroke done while painting\rendering over the image (it is the same exact color as the theathre rabbithole, the "shirt" and "leg" are just jpeg artifact type things) or something that was actually passing by, such as collectibles, or the pigeons that sometimes pass in front of sunset valley.

BTW we don't know what the whole image looks like, and that sky is'nt the sunset valley sky, the default sunsets look much different and much plainer. Heck the normal sky and water are violet, and they were so until Appaloosa Plains where it changed to cyan in the newer hoods.

There are like 7 "environments" in sims. AKA the files that have the sky and water colors as well as lighting. They are:

Violet (like ts2): Sunset Valley, Adventureland, WA destinations, Riverwiew, Barnacle Bay, Hidden Springs
Dark blue: Twinbrook, Starlight Shores, Oasis Landing
Desaturated blue almost grey: Bridgeport, Aurora Skies, Midnight Hollow
Cyan: Appaloosa Plains, Lucky Palms, Sunlit Tides, Monte Vista, Isla Paradiso, Roaring Heights
"Alien": Lunar Lakes
Teal: Dragon Valley
Light, desaturated green: Moonlight Falls, Sims University.

Each of those environments have a different sunset, and a different sunrise. None of those 7 sunsets and 7 sunrises look like the painting that you see when you load TS3, so that's actually a painting (render?) and that although it looks like a sim from the distance, is actually two wild strokes of paint.