Don't they look lovely together? Well, of course, they look good together. That's the point.
In modeling, couples can be just any two models, but there seems to be a preference for how the appearance of the two complement each other. It's not always the case, but it shows up often enough.
If the couple is modeling clothes (usually for a Fashion Magazine or ad), as in the pic at right, expect the clothes to complement each other as well, often to the point of Coordinated Clothes. Just that the guy isn't dressing that way because it'll make his girl happy. He's just being paid.
This can easily apply to families as well, even if the kids are supposed to be adopted or the family is blended. Could also apply to groups of friends, or just a large group in particular.
Remember, this is mainly for modeling, more than fiction (unless it's fiction involving modelling). Chemistry between these people isn't important, since they don't have to act. That is, unless it's part of an ad, but don't look for anything deep. They're just there to sell the product.
- At one point in Paradise Kiss, Yukari goes to do a modelling shoot with a guy. Who turns out to be her boyfriend, George. This actually really annoys her.
- Is done with Syaoran and Sakura to show their school uniforms, in little shorts narrated by Kero at the end of some episodes, or in promotional artwork.
- There's an episode of Sabrina the Teenage Witch with some sort of cute couple contest, where Libby dumps her current boyfriend and finds a new one because his hair colour complements hers better. "He was a blond. We clashed."
- Played with in Mad Men, many of the couples that fit this type have their relationships go to seed (Don/Betty, Don/Megan, Roger/Joan, Roger/Jane, Roger/Mona, Joan/Greg, and Pete/Trudy). All shiny, glamorous, movie star perfect looks above a bed of lies, abuse, hatred, manipulation, possessiveness, and anger.
- This is somewhat justified. In The Third Chimpanzee, Jared Diamond details research on subconscious selection for appearance similarities in mates. He notes that the relative length of the fourth finger has higher correlation in married couples than whether they have the same religion.
- It's lampshaded in Wraith Squadron, when Kell Tainer confesses love to Tyria Sarkin. She tells him he's Loving a Shadow, convincing himself that he loves her purely because they'd look good together, and because from an intellectual perspective they'd match too - she has no family, so he both doesn't have to deal with in-laws and can also provide her with his. He only loves the image of her. While Kell's shocked and hurt at first, he does realize that she's right.
- Lampshaded in Wicked, where Galinda and Fiyero sing "You're perfect! You're perfect! So we're perfect together!" Later subverted as Fiyero runs off with Elphaba.