>>8056123/wg/ occasionally sees whole threads dedicated to that style of pape, though more often that kind of pape will turn up in color-specific threads like this one; some Anons will also answer requests for specific colors in that style of pape
as for how they're made, some Anons make those papes manually in photoshop or some other image editor, alternatively there have been a few different projects linked to on here over time where Anons have created either a downloadable app on e.g. github, or they've made a dedicated web-based pape creation tool, where anyone can then make their own papes in that particular style, a search of the archives should find links to some/all of these projects
there's also an alternate less-commonly seen version of that style of pape that involves using 2 colors blended across a diagonal gradient
