There isn't much of a narrative. Instead, it follows various men and college students, primarily Hirokawa and Itani , in their absurdly intense attempts to catch a glimpse of women’s undergarments.
In the world of anime, "Colorful Episode 1" usually refers to one of two very different projects: the infamous late-90s comedy shorts or the deep, award-winning 2010 film. The 1999 Short Series: A Perverted Comedy Colorful Episode 1
Most people searching for Colorful today are actually looking for the directed by Keiichi Hara. While it’s a single movie, the opening sequence acts as its "Episode 1" by establishing its heavy supernatural and dramatic premise. Colorful (TV Series 1999) - IMDb There isn't much of a narrative