Octave: Setsuko gains some praise for a song she composed during a rough patch of her relationship with Yukino.
Translucent: The philosophy of Shizuka's idol, the visiting stage actress. She sees Shizuka practicing outside by herself, and figures out that the drama advisor must have asked her to hide because of her translucent syndrome acting up. The end of the chapter is the actress talking during an interview where she says she feels angst is important for a developing actress.
Arne Anka: Arne seems to belive this, with most of his work being either incredibly confusing, or dark and depressing.
Bamse: Usually, Brum's artwork is pretty cheery, but the trope was invoked in the story where he went through a "dark" period due to a rejection from a girl he liked and was promptly "discovered" as an artist.
Funky Winkerbean: The parents who don't like the drama class performing the play Wit because "School plays are for fun and relaxation, not art."
In The Life of Émile Zola, Zola insists on writing about all the injustices and social ills of French society. When the publisher that Zola works for suggests that Zola write about safer topics Zola reacts with contempt, and the publisher fires him.
Spes Phthisica: Helen's art only becomes popular when the dead landscapes of her dreams start entering into it
The Crazy Ones: Invoked by Simon in "Sydney, Australia" while he is trying to get Danny Chase, Sydney's stalker-ish former co-workernote who's subsequently slapped with a restraining order preventing him from getting withing 50 yards of Sydney until 2015 (played by Josh Groban), to sell him the rights to the saccharine love song he'd written. Simon succeeds by pointing out that the material written after Sydney broke the co-worker's heart is much better than the song he's trying to buy.
Doctor Who: In "Vincent and The Doctor", Dr Black — Bill Nighy's character — who is an art expert, explains in Van Gogh's presence how the latter managed to "transform the pain of his tormented life into ecstatic beauty" and "use [his] passion and pain to portray the joy and ecstasy and magnificence of our world". And this is why he is the greatest artist who ever lived.
Andy: 'Cause your music is sad, and depressing, and weird, and art...is supposed to happy, and fun, and everyone knows that.
Six Feet Under: Averted with everyone but Claire. Claire attains some moderate artistic success with a more upbeat portfolio, but keeps trying to pitch her own work, which is all gloomy shots of gravestones. No one is interested.
Brian from Spaced can only paint when he's unhappy. When he starts dating Twist and becomes very happy, he can't paint anymore, until someone tells him that his uncle died.
Mac Guffins Curse: Played for laughs. The Mayor's office is full of abstract paintings, and Lucas is generally unimpressed.
Lucas: "This one's called 'PAIN BEAUTIFUL PAIN' but it's just a bunch of squares. The corners could be sharp, I guess?"
Gen Urobuchi is definitely on the side of those who consider happy stories to be unrealistic, to the point where he has actually suggested that Lighter and Softer stories, by definition, contradict the laws of nature and are therefore difficult to write and impossible to believe.
"I have nothing but contempt for the deceitful thing men call 'happiness', and find myself with no choice but to push my characters, whom I pour my heart and soul out to create, into the abyss of tragedy."
Last Res0rt: Kurt "Geisha" Striaeta figured out that not only was it easier to just kidnap, rape, and petrify his victims in order to make his sculptures, it also got him better reviews from the critics too.
Fanboy dressed as Batman: I always felt Batman was best suited in the role of gritty urban crime detective? But now you guys have him up against Santas? And Easter Bunnies? I'm sorry, but that's not my Batman! The Creators: [whispering among themselves, eventually handing a note to Bat-Mite] Here, read this. Bat-Mite: Batman's rich history allows him to be interpreted in a multitude of ways. To be sure, this is a lighter incarnation, but it's certainly no less valid and true to the character's roots as the tortured avenger crying out for Mommy and Daddy. [makes the paper disappear] And besides, those Easter Bunnies looked really scary, right?! Bruce Timm (dressed as Mark Hamill's Joker): Meh.
The LEGO Movie: Wyldstyle claims that Batman is a 'true artist' because he's dark and brooding. In addition, his song is pretty much entirely about dark places and having no parents.