Calibre can be configured to use the OS defaults for reading specific file extensions. The option is buried somewhere in the preferences menu of Calibre.
On Windows, OSS SumatraPDF will read pdf, epub, djvi, fb, chm and more. You can preset 2up fullscreen & other options, including the carnival yellow default background. It's minimal and can be locked down more than Acrobat, but has still had a handful of public security vulns (much less than Acrobat), http://blog.kowalczyk.info/software/sumatrapdf/free-pdf-read...
On iOS, Marvin is an epub reading app which integrates well with Calibre and includes screen temperature adjustment (similar to Fl.ux) for reading at night.
I use Linux (mentioned though not explicitly stated in my comment above). I've dug for config options and haven't found it. I've also searched for docs and posted on several forums without finding any resolution for this.
On Windows, OSS SumatraPDF will read pdf, epub, djvi, fb, chm and more. You can preset 2up fullscreen & other options, including the carnival yellow default background. It's minimal and can be locked down more than Acrobat, but has still had a handful of public security vulns (much less than Acrobat), http://blog.kowalczyk.info/software/sumatrapdf/free-pdf-read...
On iOS, Marvin is an epub reading app which integrates well with Calibre and includes screen temperature adjustment (similar to Fl.ux) for reading at night.