I get this question a lot from fellow book lovers. The latest Kindle models, including the Paperwhite and Oasis, still use E Ink displays which are monochrome. Amazon hasn't released a color E Ink Kindle yet, though other brands like Onyx Boox have color options. The lack of color is actually a trade-off for better battery life and eye comfort during long reading sessions. E Ink color technology is improving, but currently, the screens are less sharp and more expensive. I'd love to see Amazon introduce color support for comics and illustrated books, but for now, traditional black-and-white displays remain the standard. If you're looking for color, you might consider a tablet, though it won't give you that paper-like reading experience.
For manga and graphic novel fans, this can be frustrating. While black-and-white works for most novels, some visual details get lost. I've found that Kindle's high-resolution 300ppi display at least makes grayscale art look crisp. Maybe in a few years, we'll see affordable color E Ink that doesn't sacrifice readability or battery performance.