If you are talking about color of text, see this link:
https://github.com/koreader/koreader...ries-supported
You need to switch dictionary to HTML and make a CSS file for proper styles to show up.
If you talking about pictures in dictionary entries, double check that their original files in the res folder are in color. If they are, but don’t show up as color in KOReader - report it on Github with proper logs.