Can you clarify what parts of the interface is a problem for people with color blindness? We definitely haven't put a lot of effort into accessibility features, but we also haven't gotten any feedback of where there are problems. Please feel free to file issues on GitHub for any accessibility problems you come across.
MetaCPAN doesn't have any user-based UI preferences. Any UI customizations we do have are stored with in your browser directly using localStorage. The only purpose logging in serves is to allow using ++ on modules, and customizing a few things on your author page if you have a PAUSE account. We're unlikely to add local accounts, although we are considering adding support for AuthO.