It might be the unique plot. Maybe it takes the RWBY characters and puts them in situations that are different from the original series but still in - line with the overall RWBY universe.
I'm not sure of specific fanfics similar to it off the top of my head. But you could try searching on RWBY - dedicated fanfic websites like Archive of Our Own. There are likely to be fanfics with similar themes or tones.
There's no way to really tell if it's common specifically for someone named Jojo. However, in general, reading fanfiction is a popular activity among fans of many different franchises. The Jojo series has a large and dedicated fan base, so it's likely that there are fans named Jojo who partake in reading fanfiction, but we can't say for sure how common it is without more data.
The insect bites in the lap of the king in the story might represent a disruption of the king's perceived invincibility. Kings are often seen as powerful and above common troubles. However, these insect bites show that he is still part of the natural world and subject to its whims. It could also be a way to humanize the king, making him more relatable to the readers or listeners of the story. If the story is about power dynamics, the bites could be the starting point of a change in how the king exercises his power, either because he realizes his own vulnerability or because his courtiers react differently to a king who is dealing with such a common and pesky problem.
Perhaps this Jojo is interested in exploring different interpretations and stories within the Jojo universe that fans have come up with. Fanfiction often takes the existing characters, settings, etc. from the original Jojo series and creates new and unique storylines. So, this Jojo might be a big fan of the series and wants to see what other fans have imagined.
The JoJo manga is mainly in black and white. Colored versions exist but are not the norm. Sometimes, colored illustrations are done for promotional purposes or by fans.