My son and his cousin both had their sweat tests done at an accreditted CF hospital, and their test was exactly how okok described it above. And there was no blue. Having a borderline sweat test, your son probably should have genetic testing, just to be sure. I think, from what I've read on here, that there are more than one type of sweat test, and that CFF accreditted hospitals all do it the same way.
I hope everything goes well with the test, and that you get the answers you need. Keep us posted!
I hope everything goes well with the test, and that you get the answers you need. Keep us posted!