Maybe it will eventually be possible to solve some of the issues with some sort of calibration. I doubt the inks would be absorbing 100% of the wavelengths (few materials do), so possibly adjusting the sensitivity could resolve it - if the hardware is capable.
I'm guessing not without killing the battery (already using the heart monitor during exercise uses up more battery), certain inks with certain compounds, probably block nearly all light in all frequencies from going through (certain types of true black inks)