just searching Achromatopsia + ereader brought up
http://www.achromatopsia.info/steff-...ssentials.html
where a kobo eink reader was recommended but it sounds like any non glare ereader with a large variety of font sizes might work
a lot of older eink models have been in the deals sub forum here, I personally like the $99 craig tablet it is pretty much too slow for most tablet functions but made a nice touch screen ereader for myself, even if the ability to change text or background color cannot help you, most ereader apps have a much larger selection of font sizes, embolden feature, font types than a stock ereader has