Could you please confirm the exact version of OMERO that you're using (both server and client)? 5.1.4 is the latest in the 5.1 line; 5.2.0 is the absolute latest version.
If you're using an older version, I would suggest upgrading to at least 5.1.4. You might also try checking the rendering options in the OMERO client, to see if reducing the maximum value fixes the image display. Instructions for doing this in the web client are in point 6 of
http://help.openmicroscopy.org/web-client.html; instructions for Insight are in
http://help.openmicroscopy.org/viewing- ... #rendering.
If that doesn't work, then it would be very helpful if you could send an example file to
http://qa.openmicroscopy.org.uk/qa/upload/ so that we can duplicate the problem.