My lay person theory is that the mucus has finally penetrated way deep into your lungs, and you are getting rid of stuff that has been down there a while. This happened to my on .9% saline, then again on 3% and finally on 75. Now if I skip a week, my cough diminishes. Then when I start the saline again, I go through a good week of excess coughing, finally bringing up thick, colored mucus.

If you said you were coughing up thin, clear mucus I might think it was just the 7% saline causing irritation, but the fact that it is colored means there is something in it...

Are you on antibiotics too?
Sue