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.
The Bleach manga is not colored. It's common for manga to be in black and white to focus on the line art and storytelling. Color versions might exist in certain promotions or adaptations, but the core manga is monochrome.
Generally, manga are black and white. This is mainly due to cost and production time constraints. However, some popular series might have colored pages for special chapters or volumes.
For me, MangaPark is quite good. It has a user-friendly interface and a good selection of manga. However, the legality of using free manga websites can be questionable, so be cautious.
You can search for colored manga on specialized manga websites or platforms. Some artists or groups might upload colored versions of popular manga there.
The Attack on Titan manga is mainly black and white. Coloring is rare and usually done by fans or for special editions. The original publication remains in monochrome to emphasize the detail and mood of the scenes.
Often, it's a matter of cost and effort. Coloring each panel takes a lot of resources. Also, some artists prefer the artistic expression in black and white.