Such manga is usually against ethical and moral standards. It involves content that is not suitable for public discussion or consumption. We should avoid such material.
The majority of manga are not in color. It's a common practice in the manga industry to use black and white for regular publications. But for certain limited series or special projects, color might be employed to make them stand out.
The JoJo manga is mainly presented in black and white. However, there might be some special editions or colored illustrations for promotional purposes, but the standard version is not in color.
The Uzumaki manga is not overly long or short. It's just the right length to immerse you in its creepy world. The number of volumes and pages can change based on the format you come across.