One of the great things Isao Takahata brings to his films is a wide variety of visual styles, a willingness to change the whole look of a picture several times over. It's one of his signature traits, and I don't think it's ever been more perfectly balanced than in Omohide Poro Poro. The movie's two sides - the adult Taeko spending her vacation on a farm, and the memories of her long-forgotten childhood - exist in their own worlds. The adult world is fiercely realist, the childhood world a pop montage of color and faded outlines.
These screenshots are both from Taeko-chan's childhood in the 1960s. The band in the still photo was Josie and the Tigers, a popular group in the Beatles mold. There's a strong Warhol pop spirit in this film, with advertisements, movies, and popular songs quoted and referenced freely (tapping into that nostalgia that defines so much of the Ghibli era). The second picture, with Taeko in the center, is shot as an a homage to a popular ad of the time (although, sadly, I can't remember specifics - oh, the irony).