It is a good sign!

Any form of discharge is good, that is how our body deals with extra toxins and products of unhealthy lifestyle.

But, it is always a symbol of bacterial activity.
In this case, bacteria are in simbiosis woth your body, helping cleanse.

But, it can also be a symbol of inadequat diet.

Eliminate all refined sugars and grains (go on mucusless diet), to avoid feeding bacteria. Eliminate also non-seasonal fruit.

If you think that coughing is not healthy for you (paifull lungs), you should get some natural Antibiotics , like Grapefruit seed extract, Black-Walnut and cloves tincture, tobacco leaves tincture, H2O2, Ozone, .... there are many herbs and many remedies that can be used.

Spirit

Green is good. And basically, coughing stuff up comes part and parcel with an effective cleanse; it is a sign that the epithelial layer is sloughing off...just like dead skin cells do everywhere on our bodies...consider this an exfoliation.

Green is just a sign that there is something being killed by the white blood cells that usually make our mucus clear. If you are curious, smear green sputum onto a microscope slide and view, first at 30 or 60x, then 100x assuming you suspect parasites...you'll see something in the midst of the green globs...whatever is surrounded by your fluid is the bad guy.