Supporting *Gray colorspace ICC profiles (16 bit)
Darktable does not support icc profile included a 16-bit TIFF file on import in the case of Gray colorspace
The default input profile switches to sRGB (jpg) and uses that with a warning displayed "unsupported input profile has been ignored!".
see http://www.darktable.org/redmine/issues/10040 for the initial feature request on color icc embedded profiles in TIFF.