I find that I do not suffer when reading on an eInk device for hours. In contrast, using my Ipad, Android tablet, iPhone or laptop for more than 90 minutes of reading results in my eyes starting to have issues focusing on the screen. I suspect for reading, I am concentrating on the screen much more than web browsing, watching videos, etc.
As for visualizing in colour? About the only colour over 99% of my books is the cover and I seldom spend much time looking at the cover.
BTW, you used the same link for both your papers. For the second item, did you mean to use:
E-Readers and Visual Fatigue ?