You might have luck finding colored manga on dedicated manga apps such as Comixology or Crunchyroll Manga. Sometimes, social media groups or forums focused on manga can also point you in the right direction to access colored manga.
There are several options. Some people find colored Demon Slayer manga on specialized manga forums or websites. But be careful as not all of them are legal. You could also check your local library's digital collection.
You can try some manga reading websites like MangaFox or MangaReader. But be careful as some of these might not have the legal right to distribute the content.
Social media platforms like Pinterest and Tumblr sometimes have links to colored manga. But be careful, as not all sources might be legal or of good quality.
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.